Hi, fatjuicymole.
Thank you for your response.

The cause of this problem is font familyname.
My two font files are ...
1. they have the same familyname.
2. one of my font files has only number(0 - 9).
3. the other has only alphabet(a-z, A-Z).

Maybe, Qt(or freetype) confuse.
I bond these fonts together, I get 100% success case.