I hadn't known this card until one of my French friends living in Tokyo told me about it.
Japan has 47 prefectures.
Post office in each prefecture sells a postcard shaped like foods and tourist spots representing its own culture and history.
Besides each card is available only in its prefecture!
I often go business traveling so that I am going to collect these!
The first commemorable prefecture is Hokkaido, as I went there for lessons.
Here is further info !