An upper half 11 of a tape cassette BB is made by at least a material having high transparency. Right and left holes 18a and 18b for light path are formed on side surfaces of the upper half 11. Further, roughened surfaces 10a and 10b in a prismatic shape are formed on outer right and left sides 11A1 and 11B1 or inner right and left sides 11A2 and 11B2 of the upper half 11 in neighboring areas of or adjacent to the right and left holes 18a and 18b.