In a tape cassette, which comprises a cassette casing which consists of upper and lower halves which are molded by injection molding from a synthetic resin, reels mounted for rotation in the cassette casing and having at least lower flanges, and a groove formed in an outer surface of a bottom wall of the lower half in a region which is adjacent the lower flanges of the reels, an improvement comprises at least a projection being formed on at least a portion of an inner surface for the bottom wall of the lower half which overlies the guide groove so as to facilitate a flow of a molten resin injection near the guide groove during molding of the lower half. |