Many publishers and academic societies permit authors of articles published in academic journals to make the full text available in institutional repositories or their personal website.
However, if you have agreed to transfer the copyright of your article to the publisher or academic society, there may be restrictions on the versions that can be deposited in institutional repositories, as well as embargo periods (restrictions on the timing of public availability).
For detailed information on copyright when depositing academic journal articles in the UTokyo Repository, please refer to the following articles on the UTokyo Open Science Portal.