To provide an offset compensating circuit for an encoder having a simple structure and few influence of noise that can execute stable offset compensation and detection with high solution.

Each peak value max of an A-phase signal of sine wave signals in two phases having a phase difference of 90 degrees, an A'-phase signal of the reversed signal to the referential voltage of the A-phase signal, a B-phase signal of the sine wave signals, and a B'-phase signal of the reversed signal to the referential voltage of the B-phase signal is sampled at the prescribed angle detecting value of an angle detecting signal by interpolation processing to create sine wave signals, and then the difference of each peak value is calculated. The offset error is detected to be provided the feedback to the sine wave signals in the two phases. Thereby the offset of the encoder is compensated. Each offset error of the A-phase and the B-phase obtained in a subtracting circuit is integrated to be then averaged.