Just opposite the Nishi Tenma postoffice is YOD Gallery. I walk past it everyday on my commute to the office, so I popped in just last week to see Hintobi, "Dignity and Beauty" (more info here).
The gallery itself is a single room not more than 4 or 5 meters wide, but still seems that you can pack a lot of art in there. A noticable feature of YOD is the wide wall outside the building, which acts as a canvas for the exhibiting artist to advertise on. I've heard that it's even used for live painting sometimes!
Keep an eye on upcoming exhibitions. As it's in a great area for a bit of an art stroll, you can add it to the list of galleries you're going to see.