A tape cassette device comprises a cassette case in which a stationary reel with a tape guide path is housed, and an endless tape wound on the outer circumference of said stationary reel, the innermost part drawn out along said guide path to the inside of said stationary reel to be wound on the outer circumference of said stationary reel. Said case has a bottom plate having a scanning head and a tape drive mechanism inserting opening located at the inside of said stationary reel. A pair of sliders are disposed inside said cassette case, which are displaceable between a lower position where it is located at the side of said bottom plate for closing said opening and an upper position where it is located away from said bottom plate for opening said opening.