PURPOSE: To have a fired linear speed with high accuracy and with a simple constitution, by giving the feedback control in accordance with a variance of the number of revolution of a motor that gives revolutions with a linear speed to a disk with a pickup, via a potentiometer, a divider circuit, etc.

CONSTITUTION: The degree of shift of a pickup 3 is detected toward the radius direction of a disk 1 via a potentiometer 4. This detected voltage is processed by a divider circuit 5 and turned into the signal corresponding to the linear speed of the disk 1 with the pickup 3. Thus the number of revolution of a driving motor 2 is controlled for the disk 1 via an amplifier 6 and an adder 10. At the same time, the revolution of the motor 2 is detected by a frequency generator 7. Then the feedback control is carried out to a variance of revolution so that the motor 2 corresponds to the linear speed via adders 9 and 10 to obtain a coincidence between the output voltage of the circuit 5 and that of a frequency-voltage converting circuit 8 and obtained in accordance with the value detected by the generator 7. With this simple constitution, the linear speed of the disk 1 can be set constant with high accuracy, without affecting the potentiometer, the divider circuit, etc.