I was wrong on fuse box.
I found all the fuses there are good. That means it can not be the fuse box for fans. Since both the ceiling fan and toilet fan are out, it cannot be the broken fan. By the way, the fuse in the ceiling fan is good.
Now there are two possibilities left. First one, maybe the installer put the fuse box somewhere I can see only if I break the wall on the exact location. The second, it does not have a fuse at all. But both do not make sense at all.
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