Magnetic tape cassette

A magnetic tape cassette used in an apparatus having a light source and a light sensor for detecting a tape end of a magnetic tape being loaded therein, the magnetic tape cassette comprising:

• a cassette housing being formed by combining an upper half and a lower half made of transparent or semi-transparent material, wherein the cassette housing is equipped with a reel being connected to the magnetic tape through an intermediary leader tape having higher light transmittance than the magnetic tape for winding up the magnetic tape;
• a light exit being opposed to the light sensor when the magnetic tape cassette is loaded to a predetermined position in the apparatus, for passing light from the light source to the light sensor through the light exit, wherein a light path of the light emitted from the light source crosses a travel path of the magnetic tape;
• a rib being formed in the upper half and the lower half wherein a plurality of triangular shaped prisms are formed serially on at least one side surface of the rib placed between the light source and the light exit;
• and
• a light-shielding member formed separately from the rib and placed contiguous to the rib, having a light window for passing the light emitted from the light source through the light exit.