@Kiril I'm very sorry for asking this question again.
I found that binwalk shows nothing with this firmware. When I searched on Google, it happens when firmware's entropy is all random(means firmware is encrypted) or it's just bunch of strings.
When I check entropy, I can see that the former is not this case. But I think the latter is also not this case.
How should I progress this one? I'm really really sorry because I'm ungeek(?)