diff --git a/d3rlpy/logging/logger.py b/d3rlpy/logging/logger.py
index 61ccdad5..3792c947 100644
--- a/d3rlpy/logging/logger.py
+++ b/d3rlpy/logging/logger.py
@@ -90,12 +90,11 @@ def write_histogram(
     ) -> None:
         r"""Writes histogram.
 
-        # TODO
         Args:
-            epoch:
-            step:
-            name:
-            values:
+            epoch: Epoch.
+            step: Training step.
+            name: Histogram name.
+            values: Histogram values.
         """
 
     def after_write_metric(self, epoch: int, step: int) -> None:
@@ -120,7 +119,12 @@ def close(self) -> None:
     def watch_model(
         self, logging_steps: int, algo: TorchModuleProtocol
     ) -> None:
-        r"""TODO: Docstring and type"""
+        r"""Watch model parameters / gradients during training.
+
+        Args:
+            logging_steps: Training step.
+            algo: Algorithm.
+        """
 
 
 class LoggerAdapterFactory(Protocol):
@@ -214,5 +218,5 @@ def measure_time(self, name: str) -> Iterator[None]:
     def adapter(self) -> LoggerAdapter:
         return self._adapter
 
-    def watch_model(self, logging_steps, algo: TorchModuleProtocol) -> None:
+    def watch_model(self, logging_steps: int, algo: TorchModuleProtocol) -> None:
         self._adapter.watch_model(logging_steps, algo)
diff --git a/tests/logging/test_logger.py b/tests/logging/test_logger.py
index 55ca4443..ec4dd99e 100644
--- a/tests/logging/test_logger.py
+++ b/tests/logging/test_logger.py
@@ -1,9 +1,11 @@
 from typing import Any, Dict
 
+import numpy as np
 import pytest
 
 from d3rlpy.logging import D3RLPyLogger
 from d3rlpy.logging.logger import SaveProtocol
+from d3rlpy.types import Float32NDArray
 
 
 class StubLoggerAdapter:
@@ -12,6 +14,7 @@ def __init__(self, experiment_name: str):
         self.is_write_params_called = False
         self.is_before_write_metric_called = False
         self.is_write_metric_called = False
+        self.is_write_histogram_called = False
         self.is_after_write_metric_called = False
         self.is_save_model_called = False
         self.is_close_called = False
@@ -28,6 +31,11 @@ def write_metric(
         assert self.is_before_write_metric_called
         self.is_write_metric_called = True
 
+    def write_histogram(
+        self, epoch: int, step: int, name: str, values: Float32NDArray
+    ) -> None:
+        self.is_write_histogram_called = True
+
     def after_write_metric(self, epoch: int, step: int) -> None:
         assert self.is_before_write_metric_called
         assert self.is_write_metric_called
@@ -67,17 +75,20 @@ def test_d3rlpy_logger(with_timestamp: bool) -> None:
     assert adapter.is_write_params_called
 
     logger.add_metric("test", 1)
+    logger.add_histogram("test", np.array([1.0], dtype=np.float32))
     with logger.measure_time("test"):
         pass
 
     assert not adapter.is_before_write_metric_called
     assert not adapter.is_write_metric_called
+    assert not adapter.is_write_histogram_called
     assert not adapter.is_after_write_metric_called
     metrics = logger.commit(1, 1)
     assert "test" in metrics
     assert "time_test" in metrics
     assert adapter.is_before_write_metric_called
     assert adapter.is_write_metric_called
+    assert adapter.is_write_histogram_called
     assert adapter.is_after_write_metric_called
 
     assert not adapter.is_save_model_called