Most likely an early 16th century ( 1500's ? period ) European wheellock Arquebus design.....
Probably of spanish or italian origin, judging by the embellishments on the stock. Possibly french as well....
German arms of this period, I believe were rarely adorned with such.... usually more simple and utilitarian, typical of german design.
I may be wrong, but I also don't think the japanese ever used wheellock designs. They would have been matchlock firearms, as trade with the outside world pretty much didn't exist in japan, Until Admiral Perry sailed into Edo bay, in 1853... forcibly opening the country, so to speak.
Hard to say with any certainty from such a small image. It may just LOOK like a wheellock, and that may be simply designs on the stock..
Also, "technically" by definition, an Arquebus would be a matchlock firearm, not wheellock but who's to know when this particular gun was actually made.... could be 10 years old theoretically
Interesting picture though.. where'd you find it ?