PURPOSE: To limit the rotational speed of a turntable, and to prevent a disk from being damaged, by comparing the rotational speed of the disk with that of the turntable at the time of starting and stopping the disk, and decreasing the acceleration of the turntable, when the difference of both the speeds exceeds a set value.
CONSTITUTION: The turntable 2 of the disk device is driven to rotate by a motor 4, and an optical disk medium 3 is pressed against the table 2 by a clamper 1 and rotated. The rotation of this medium 3 is monitored by a phototransistor TR 6, and a voltage being proportional to a rotational frequency is applied to a deciding circuit 9 by a F/V converter 7. Also, the rotational frequency of the table 2 is detected by an optical tachometer 5, and a voltage being proportional to its rotational frequency is applied to the deciding circuit 9 from an F/V converter 8. By this deciding circuit 9, the difference of the rotational frequency of the table 2 and the medium 3 is derived, and whether its difference exceeds a prescribed value or not is decided. When the rotational frequency exceeds the prescribed value, the motor 4 is controlled by a motor driving part 10, and the rotational speed of the table 2 is limited.