Hi @Kensuke Kuroda ,
Only Jira admins who have the Administer Jira global permission can create projects in Jira. Please make sure that you have Jira admin permissions.
1. For Server instance you will be able to create Project from Projects Dropdown. Refer below screenshot.
2. For Atlassian cloud instance please refer below screenshot.
If you do not see above options then you need to reach out to your internal Jira admin to do this.
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