The cassette half molding method molds one of upper and lower halves of the magnetic tape cassette by injection molding with an injection mold in which a gas vent pin for smoothing a flow of molten resin to be introduced in the cavity for molding a transparent or semitransparent window portion provided in the upper half. The cassette half is molded by this molding method. The magnetic tape cassette has a friction sheet interposed either between a pair of take-up hubs and the upper half, or between the pair of take-up hubs and the lower half, or both, and the friction sheet is made of polyethylene-based resin and has a surface electric resistance value in the range of 1×107&OHgr; to 1×1010&OHgr;. The magnetic tape cassette has a rib for reducing a resistance when the roller of the detecting member passes through which is provided at a position corresponding to a recess and on a side of the front lid in the top surface of the body case.