Previous version of OSX? Lion? Snow Leopard?
Source of your fonts - OSX included fonts, fonts collected over the years?
Do you use a Font Manager other than FontBook?
Font Problems can be a conflict between two or more fonts, a damaged or outdated font, OR a corrupt font cache.
Tackle font problems using OS X Lion's Font list
Font Management in OS X
SNIP So here is one way to reset Font Book in Snow Leopard, 10.6.x through Mountain Lion, 10.8.x.
1) Restart your Mac and immediately hold down the Shift key when you hear the startup chime to boot into Safe Mode. Keep holding the Shift key until OS X asks you to log in (you will get this screen on a Safe Mode boot even if your Mac is set to automatically log in). Let the Mac finish booting to the desktop and then restart normally. This will clear Font Book's database and the cache files for the user account you logged into in Safe Mode.
In Leopard or earlier, any font sets you have created will be gone. Also, all fonts in the three main Fonts folders (System, Library, your user account) will now be active, regardless of their state beforehand.
2) Clear all font cache files from the system and restart. The Terminal method for this is explained at the very end of section 17. The next time you launch Font Book, it will create a new database.
Mac OS X 10.7 Lion & fonts
What's new in Lion: fonts and text
Thank you very much for your advice. My previous version is Lion. I am a novice in font management, I will try your suggestions.
Resetting font book worked ! Thank you