Blog URL not behaving — how to fix trailing slash problem

My WP blog URL works only with a trailing slash. This means internal links also are messed up. I suspect this is a problem with my server settings, rather than WP, but if someone would be kind enough to tell me how to fix it/what to look for I’d much appreciate it.

WP URL: http://royzemi.rikkyo.ac.jp/magazine takes you to:
http://www.fangorn.local/magazine/ (server name)

But it works with a trailing slash: http://royzemi.rikkyo.ac.jp/magazine/

This is a simple Mac OS X box (not OS X server), running 10.5