PURPOSE: To cancell unevenness of rotation by a method wherein the title circuit is provided with a detecting circuit for detecting the constitution of the unevenness of rotation, a sine wave generating circuit, generating a sine wave having a frequency same as the frequency constituent detected by the detecting circuit, and a corrector, correcting the phase and the level of the sine wave.

CONSTITUTION: The analog error output signal D of a D/A converter 5 is inputted into a driving circuit 6 and a detector 9. Then, only the set frequency constituent of the detector is extracted. The corrector 10 receives a D/A converter output signal and a sine wave generating circuit output signal and converts the sine wave into a sine wave signal E, having the same phase and level as the constituent of unevenness of rotation, which comes from the D/A converter, while the sine wave signal E is mixed with a reference voltage C from a reference voltage generating circuit 7 in a mixer 11 to supply it to a driving circuit 6 and compare it with the output voltage of the D/A converter 5.