This paper describes a low distortion sine wave oscillator. It is known that there are the distortion that comes from gain control circuit and characteristic of the devices in the state variable oscillator. To decrease the distortion, the automatic gain control circuit (AGC circuit) using square add method that is composed of analog multiplier is proposed and examined. Square add method can be applied to 2phase oscillator and 3phase oscillator. The output signal of AGC circuit using square add method has distortion that comes from the error between 2phase or 3phase alternating current. And 3phase AGC circuit has lower distortion than 2phase AGC circuit. The THD of 3phase oscillator using the AGC circuit is -135.2dB that is signal of low distortion.