diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 608717d6..d2919a9f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -10,18 +10,15 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: [3.6, 3.7, 3.8]
-        include:
-          - os: ubuntu-20.04
-            python-version: 3.6
-        exclude:
-          - os: ubuntu-latest
-            python-version: 3.6
+        python-version:
+          - '3.8'
+          - '3.10'
+          - '3.12'
 
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Set up Python
       uses: actions/setup-python@v4
diff --git a/onlinejudge_command/subcommand/generate_input.py b/onlinejudge_command/subcommand/generate_input.py
index 2aa47496..cbeea835 100644
--- a/onlinejudge_command/subcommand/generate_input.py
+++ b/onlinejudge_command/subcommand/generate_input.py
@@ -71,7 +71,7 @@ def submit(f, *args, **kwargs):
 
 def write_result(input_data: bytes, output_data: Optional[bytes], *, input_path: pathlib.Path, output_path: pathlib.Path, print_data: bool, lock: Optional[threading.Lock] = None) -> None:
     # acquire lock to print logs properly, if in parallel
-    nullcontext = contextlib.ExitStack()  # TODO: use contextlib.nullcontext after Python 3.7
+    nullcontext = contextlib.nullcontext()
     with lock or nullcontext:
 
         if not input_path.parent.is_dir():
@@ -125,7 +125,7 @@ def check_randomness_of_generator(input_data: bytes, *, name: str, lock: Optiona
         return None
 
     input_digest = hashlib.sha1(input_data).digest()
-    nullcontext = contextlib.ExitStack()  # TODO: use contextlib.nullcontext after Python 3.7
+    nullcontext = contextlib.nullcontext()
     with lock or nullcontext:
         if len(generated_input_hashes) < limit:
             if input_digest in generated_input_hashes:
diff --git a/onlinejudge_command/subcommand/test.py b/onlinejudge_command/subcommand/test.py
index 4945a7a7..e4587012 100644
--- a/onlinejudge_command/subcommand/test.py
+++ b/onlinejudge_command/subcommand/test.py
@@ -255,8 +255,8 @@ def test_single_case(test_name: str, test_input_path: pathlib.Path, test_output_
         elapsed: float = info['elapsed']
         memory: Optional[float] = info['memory']
 
-    # lock is require to avoid mixing logs if in parallel
-    nullcontext = contextlib.ExitStack()  # TODO: use contextlib.nullcontext() after updating Python to 3.7
+    # lock is required to avoid mixing logs if in parallel
+    nullcontext = contextlib.nullcontext()
     with lock or nullcontext:
         if lock is not None:
             logger.info('')
diff --git a/onlinejudge_command/utils.py b/onlinejudge_command/utils.py
index 4f404011..24c420d6 100644
--- a/onlinejudge_command/utils.py
+++ b/onlinejudge_command/utils.py
@@ -190,10 +190,7 @@ def webbrowser_register_explorer_exe() -> None:
     if not is_windows_subsystem_for_linux():
         return
     instance = webbrowser.GenericBrowser('explorer.exe')
-    if sys.version_info < (3, 7):
-        webbrowser.register('explorer', None, instance)  # TODO: remove this after Python 3.6 supprot is finished
-    else:
-        webbrowser.register('explorer', None, instance, preferred=True)  # `preferred=True` solves the issue that terminal logs are cleared on cmd.exe with stopping using wslview via www-browser. TODO: remove `preferred=True` after https://github.com/wslutilities/wslu/issues/199 is fixed.
+    webbrowser.register('explorer', None, instance, preferred=True)  # `preferred=True` solves the issue that terminal logs are cleared on cmd.exe with stopping using wslview via www-browser. TODO: remove `preferred=True` after https://github.com/wslutilities/wslu/issues/199 is fixed.
 
 
 def get_default_command() -> str:
diff --git a/setup.cfg b/setup.cfg
index bcc72cea..2c6a3e84 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -7,8 +7,9 @@ classifiers =
     Intended Audience :: Developers
     License :: OSI Approved :: MIT License
     Operating System :: OS Independent
-    Programming Language :: Python :: 3.5
-    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.10
+    Programming Language :: Python :: 3.12
     Topic :: Internet :: WWW/HTTP
     Topic :: Software Development
     Topic :: Text Processing :: Markup :: HTML
diff --git a/setup.py b/setup.py
index 37665f5d..e36d7049 100755
--- a/setup.py
+++ b/setup.py
@@ -11,7 +11,7 @@
     url=version.__url__,
     license=version.__license__,
     description=version.__description__,
-    python_requires='>=3.6',
+    python_requires='>=3.8',
     install_requires=[
         'online-judge-api-client >= 10.9.0, < 11',
         'colorama >= 0.3, < 1',