diff --git a/d3rlpy/algos/qlearning/base.py b/d3rlpy/algos/qlearning/base.py
index daea46db..e2517961 100644
--- a/d3rlpy/algos/qlearning/base.py
+++ b/d3rlpy/algos/qlearning/base.py
@@ -525,7 +525,7 @@ def fitter(
         # save hyperparameters
         save_config(self, logger)
 
-        logger.watch_model(0, 0, gradient_logging_steps, self)  # type: ignore
+        logger.watch_model(0, 0, gradient_logging_steps, self)
 
         # training loop
         n_epochs = n_steps // n_steps_per_epoch
@@ -566,7 +566,9 @@ def fitter(
 
                 total_step += 1
 
-                logger.watch_model(epoch, total_step, gradient_logging_steps, self)  # type: ignore
+                logger.watch_model(
+                    epoch, total_step, gradient_logging_steps, self
+                )
 
                 if (
                     logging_strategy == LoggingStrategy.STEPS
@@ -684,7 +686,7 @@ def fit_online(
         # save hyperparameters
         save_config(self, logger)
 
-        logger.watch_model(0, 0, gradient_logging_steps, self)  # type: ignore
+        logger.watch_model(0, 0, gradient_logging_steps, self)
 
         # switch based on show_progress flag
         xrange = trange if show_progress else range
@@ -754,7 +756,9 @@ def fit_online(
                             for name, val in loss.items():
                                 logger.add_metric(name, val)
 
-                        logger.watch_model(epoch, total_step, gradient_logging_steps, self)  # type: ignore
+                        logger.watch_model(
+                            epoch, total_step, gradient_logging_steps, self
+                        )
 
                         if (
                             logging_strategy == LoggingStrategy.STEPS
diff --git a/d3rlpy/logging/file_adapter.py b/d3rlpy/logging/file_adapter.py
index fbcf19a8..cc87d8a4 100644
--- a/d3rlpy/logging/file_adapter.py
+++ b/d3rlpy/logging/file_adapter.py
@@ -7,10 +7,10 @@
 
 from .logger import (
     LOG,
+    AlgProtocol,
     LoggerAdapter,
     LoggerAdapterFactory,
     SaveProtocol,
-    TorchModuleProtocol,
 )
 
 __all__ = ["FileAdapter", "FileAdapterFactory"]
@@ -87,8 +87,9 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
+        assert algo.impl
         if logging_steps is not None and step % logging_steps == 0:
             for name, grad in algo.impl.modules.get_gradients():
                 path = os.path.join(self._logdir, f"{name}_grad.csv")
diff --git a/d3rlpy/logging/logger.py b/d3rlpy/logging/logger.py
index ba289831..a0cb152f 100644
--- a/d3rlpy/logging/logger.py
+++ b/d3rlpy/logging/logger.py
@@ -48,11 +48,15 @@ def get_gradients(self) -> Iterator[Tuple[str, Float32NDArray]]: ...
 
 
 class ImplProtocol(Protocol):
-    modules: ModuleProtocol
+    @property
+    def modules(self) -> ModuleProtocol:
+        raise NotImplementedError
 
 
-class TorchModuleProtocol(Protocol):
-    impl: ImplProtocol
+class AlgProtocol(Protocol):
+    @property
+    def impl(self) -> Optional[ImplProtocol]:
+        raise NotImplementedError
 
 
 class LoggerAdapter(Protocol):
@@ -109,7 +113,7 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
         r"""Watch model parameters / gradients during training.
 
@@ -209,6 +213,6 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
         self._adapter.watch_model(epoch, step, logging_steps, algo)
diff --git a/d3rlpy/logging/noop_adapter.py b/d3rlpy/logging/noop_adapter.py
index aa4ece67..de01eec0 100644
--- a/d3rlpy/logging/noop_adapter.py
+++ b/d3rlpy/logging/noop_adapter.py
@@ -1,10 +1,10 @@
 from typing import Any, Dict, Optional
 
 from .logger import (
+    AlgProtocol,
     LoggerAdapter,
     LoggerAdapterFactory,
     SaveProtocol,
-    TorchModuleProtocol,
 )
 
 __all__ = ["NoopAdapter", "NoopAdapterFactory"]
@@ -42,7 +42,7 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
         pass
 
diff --git a/d3rlpy/logging/tensorboard_adapter.py b/d3rlpy/logging/tensorboard_adapter.py
index 28ec646f..ba248785 100644
--- a/d3rlpy/logging/tensorboard_adapter.py
+++ b/d3rlpy/logging/tensorboard_adapter.py
@@ -4,10 +4,10 @@
 import numpy as np
 
 from .logger import (
+    AlgProtocol,
     LoggerAdapter,
     LoggerAdapterFactory,
     SaveProtocol,
-    TorchModuleProtocol,
 )
 
 __all__ = ["TensorboardAdapter", "TensorboardAdapterFactory"]
@@ -74,8 +74,9 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
+        assert algo.impl
         if logging_steps is not None and step % logging_steps == 0:
             for name, grad in algo.impl.modules.get_gradients():
                 self._writer.add_histogram(
diff --git a/d3rlpy/logging/utils.py b/d3rlpy/logging/utils.py
index 467d1e33..81412395 100644
--- a/d3rlpy/logging/utils.py
+++ b/d3rlpy/logging/utils.py
@@ -1,10 +1,10 @@
 from typing import Any, Dict, Optional, Sequence
 
 from .logger import (
+    AlgProtocol,
     LoggerAdapter,
     LoggerAdapterFactory,
     SaveProtocol,
-    TorchModuleProtocol,
 )
 
 __all__ = ["CombineAdapter", "CombineAdapterFactory"]
@@ -54,7 +54,7 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
         for adapter in self._adapters:
             adapter.watch_model(epoch, step, logging_steps, algo)
diff --git a/d3rlpy/logging/wandb_adapter.py b/d3rlpy/logging/wandb_adapter.py
index 08813eb2..4e388a26 100644
--- a/d3rlpy/logging/wandb_adapter.py
+++ b/d3rlpy/logging/wandb_adapter.py
@@ -1,10 +1,10 @@
 from typing import Any, Dict, Optional
 
 from .logger import (
+    AlgProtocol,
     LoggerAdapter,
     LoggerAdapterFactory,
     SaveProtocol,
-    TorchModuleProtocol,
 )
 
 __all__ = ["WanDBAdapter", "WanDBAdapterFactory"]
@@ -63,9 +63,10 @@ def watch_model(
         epoch: int,
         step: int,
         logging_steps: Optional[int],
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
         if not self._is_model_watched:
+            assert algo.impl
             self.run.watch(
                 tuple(algo.impl.modules.get_torch_modules().values()),
                 log="gradients",
diff --git a/tests/logging/test_logger.py b/tests/logging/test_logger.py
index c9584682..9b3ec0f0 100644
--- a/tests/logging/test_logger.py
+++ b/tests/logging/test_logger.py
@@ -4,7 +4,7 @@
 from torch import nn
 
 from d3rlpy.logging import D3RLPyLogger
-from d3rlpy.logging.logger import SaveProtocol, TorchModuleProtocol
+from d3rlpy.logging.logger import AlgProtocol, SaveProtocol
 
 
 class StubLoggerAdapter:
@@ -46,7 +46,7 @@ def watch_model(
         epoch: int,
         step: int,
         logging_step: int,
-        algo: TorchModuleProtocol,
+        algo: AlgProtocol,
     ) -> None:
         self.is_watch_model_called = True