In a tape cassette (5) to be used for a tape printing device (1), a roll part T0 of a print tape T having a preset tape width is firmly attached to the under surface of a rotation support section (21a) of a tape unit (20) by a lower spool (22). The tape unit (20) is provided with a tape identification section (30) for identifying the type etc. of the rolled tape. In the tape identification section (30), a vertical through hole (61) as a tape width identification part is provided varying its position depending on the tape width. Meanwhile, a cassette case body (32) and a cassette cover (33) of the tape cassette (5) are provided with a tape detection part (50a, 50b) to which the tape identification section (30) can be set or attached, while being provided with a projection (52) as a tape width detection part to be paired with the vertical through hole (61) so that only a tape unit (20) including a rolled print tape having a preset tape width is allowed to be attached to the tape cassette (5). By the composition, erroneous loading of an improper tape unit (20) (to which a tape of a different width has been set) in the tape cassette (5) can be prevented.
