O21 Or J10 German Stamp

More likely Bavaria 187

Rather than take wild swings at guessing (Germany has no J10, Germany O21 is also red stamp but with a completely different design; the Japan stamp you posted is no way an airmail) I recommend you see the identifier at
http://www.stampsmarter.com/feature...eatures.html
scroll down to "World ID" and click on it. This will help you identify the country.

Then go to stampworld.com and try to pin down the stamp ID. They (usually) give Scott numbers (at least in the English version) and pricing that you can use as a very rough guide.

If that fails, then try this site.

Hi Hy-brasil , I did do exactly that and J10 and O21 is what I got from Stampworld. But I think Willwood42 might also be right that the Bavaria 187 is just like my stamp. Thank you very much guys !

Your Bavarian 80 pf stamp (Scott #187) is listed in the Stampworld catalogue as Bavaria no.149.

The Stampworld catalogue does not use Scott numbers, but has its own numbering system.

" How do I read the numbers?
Our catalogue number system is solely based on the day and country of issue. It starts with "1" for the first stamp issued in the particular country and then continues up for each new issue. There are a few instances where stamps of the same type or motive have been gathered under one number. Numbers could then be Spain 25, 25A, 25B, 25C. "