Abstract: A circuit for controlling the speed of a magnetic tape reel motor of an audio signal recording/playing mechanism. The circuit is based on the fact that the reel revolution period varies at a constant rate per revolution. The circuit measures the frequency generating value of the tape reel motor running at the normal speed to generate the ideal pulse value of the normally running motor as the initial reference value. Then the tape reel motor is run at the speed of N times the normal speed. The output of constant value means is added to the initial reference value to obtain the ideal pulse value. The present frequency generating value measured is compared with the ideal pulse value, which result is used to increase or decrease the applied voltage of the tape reel motor.