Most of your comments are in japanese... Are you using a legal japanese version of RMXP, or have you pirated it?
Anyways, the problem is that you're trying to set the font size for timers to something which is "Unknown at [that] time". This isn't working.
You might want to create a new project and compare the "Main" of that with your current one.
Also, it'd be nice if you could post the code used in the related classes, rather than a demo. This is for your own sake as well, as it would be ridiculously easy to steal your work, which has been known to happen.