Hey there @kito.hirokazu welcome to the community!
This looks like an opaque access token - If you need to decode it at all, you’ll need to include an audience param when constructing the /authorize request. It depends on how you are initiating authorization, but the audience is typically set when configuring Auth0 - For example AuthorizationParams in auth0-react.
The following FAQs should be of use:
https://community.auth0.com/t/why-is-my-access-token-not-a-jwt-opaque-token/31028
https://community.auth0.com/t/what-is-the-audience/71414