Good evening Nobusuke! Sounds like a great event ...
You can create an event page using your OSGeo ID (
https://id.osgeo.org/ldap/create) to sign into the website.
Depending on what you want to work on you may need to request an additional
role as outlined here:
Dear list,
I'm from OSGeo Japan Chapter.
We will hold FOSS4G local event in Japan and would like to create an
information page in OSGeo.org website. Can I make web page by myself or
ask to someone?
And one of the conference (FOSS4G Niigata) had released registration form.
