PURPOSE: To automatically detect a difference of a tape in thickness and to drive the tape with proper tape tension by providing a device for detecting a hole, a through hole or a notch, etc., for detecting tape thickness provided in a tape cassette.

CONSTITUTION: The tape cassette 21 is formed by combining vertically and upper half 22 with a lower half 23, incorporating a take-up reel 1, a supply reel 2 and a tape, etc., inside. Then, detecting parts 24, 25 and 26 consisting of a through hold and holes in the upward direction, arranged in the direction of right angles with a connecting line between rotary shafts of the reel 1 and the reel 2 are provided in approximately the middle of the bottom surface. Then, the detecting part 24 has a through hole (passing through the lower half 23), while the detecting parts 25 and 26 have holes (without passing through the lower half 23). Then, actuators 28, 29 and 30 of a microswitch 27 as the detecting device of the lower part of the cassette half 23 are correspondingly operated, and a tape thickness discriminating switch is operated by the actuator 28. By this method, the tape tension is automatically changed by the thickness of the tape to enable the tape to travel stably.