This train is in front of the National Museum of Nature and Science in Tokyo, and its gift shop also sells cards with it, and right now I am the happy owner of one :)
This D51 class steam locomotive is a type of 2-8-2 steam locomotive built by the Japanese Government Railways, the Japanese National Railways and various manufacturers from 1936 to 1951. The name consists of a "D" for the four sets of driving wheels and the class number 51 for tender locomotives that the numbers 50 through 99 were assigned to under the 1928 locomotive classification rule. This one here particularly shows a D 51 231 model.
the stamp is from the Endangered fauna set of 5 stamps issued in 2011.
Thanks a lot to Maggie for pointing it out coz she knows I always have problems with locating the Japanese stamps :D
And thanks so much again for the fantastic surprise!!