PURPOSE: To secure an easy increase of the revolution number of the rotary head by a desired amount by controlling the electromagnetic brake through adoption of the electromagnetic braking system to the disc servo.

CONSTITUTION: The rotary head is rotated in a higher speed (30 or 45Hz) than 30Hz via disc motor 18 and elastic belt 20. And FF2 is actuated by the pulse signal which is induced to the tachohead 1 through rotations of steel bar 15. With the output of FF2, trapezoid wave generator circuit 3 is actuated. Then the output of circuit 3 is compared 6 with reference signal 7, and comparison output 9 is applied to compound circuit 16. And electromagnetic brake 19 is controlled via amplifier circuit 17 to set the revolution of the rotary head to 30Hz, and at the same time the phase is synchronized with signal 7.