The present invention provides a novel structure of a tape cartridge (10) accommodating a printing tape (T) and an ink ribbon (R) used for printing, which prevents the printing tape from being stuck in a cartridge case or the ink ribbon (R) from being slackened. The tape cartridge (10) of the invention has a mechanism for preventing an end of the tape from being reversely moved back into the cartridge case. A typical structure of the mechanism includes an anti-inversion system which prevents a tape core having a tape wound thereon from rotating in a reverse direction, that is, a direction opposite to a normal rotating direction for printing. The anti-inversion effects are removed when the tape cartridge (10) is set in a printing device such as a tape writer to ensure smooth feeding of the tape for printing. When the tape is forcibly pressed back into the cartridge case, a movable platen clamps the tape between the platen and a fixed wall to prevent reverse movement of the tape. The tape cartridge of the invention also includes an anti-slack mechanism for preventing slack of the ink ribbon (R) through engagement of a ribbon winding core with an anti-rotational engagement piece. Engagement of this anti-slack mechanism is also released when the tape cartridge is set in the printing device.