Tape cassette drive assembly

A device for stably running a magnetic recording tape of a tape cassette comprises a reel shaft and a motor connected to the reel shaft. The reel shaft and the motor make a running of the magnetic recording tape providing back tension exerted on the magnetic recording tape. Within the housing of the tape cassette, a first lever having one end rotatably fixed to the housing is mounted. A guide roller for guiding the running direction of the tape is rotatably fixed to another end of the first lever. Therefore, the first lever may swing in response to a back tension exerted on the tape. An amount of the swing of the first lever is detected by a second lever which is rotably located out of the housing and selectably engaged with the first lever. The second lever is connected to the detection means which generates an electric signal in accordance with the amount of rotation of the second lever. The electric signal is sent to the electric controlling circuit means electrically connected to the motor. The electric controlling circuit means controls a value of the voltage supplied to the motor in accordance with the electric signal, and stabilize the value of the back tension exerted to the tape via the motor and the reel shaft.