In two rooms - Room-101 on the 1st floor (just to the left as you come in the entrance to the Ginza Okuno Building) and in Room-508. The 508 space is basically an art gallery, and the 101 space is half-art gallery and half antique shop. Recently the owner (artist, graphic designer, and antique collector) is producing very interesting fusion art consisting of antique and vintage objects merged with his original art. The artist/antique collector/owner is also quite knowledgeable and passionate about antiques.
The Okuno Building is a great place for a shop selling cool old stuff, as the building itself is quite old (by Tokyo standards in any case!) - half build in 1932 and half in 1934.
The website for Y's ARTS is:
Lyle (Hiroshi) Saxon