A tape cassette has a cassette case with top face, under face, front face, rear face, and a pair of right and left side face portions. A pair of supply and take-up tape containers sides is provided in the cassette case. A tape is wound around a pair of reels and contained in the pair of tape containers. A first wall portion connects the rear and right side face portion with each other and forms part of the take-up side tape container. A second wall portion connects the rear and left side face portion with each other and forms part of the supply side tape container. A first prism portion extends from the rear face portion to the right side face portion and refracts or reflects light from a light emission element of a recording and reproducing apparatus for detecting presence and absence of the tape cassette.