To accurately correct a torque value of a scroll compressor.

In a laden state wherein a scroll compressor is rotating, a laden torque measurement process (S4) measuring a laden torque value with a measuring device from a motor current based upon a load received by an AC servomotor is performed. In unladen state wherein only a shaft rotating unit is working, an unladen torque measurement process (S7) measuring an unladen torque value with a measuring device from a motor current based upon a load received by the AC servomotor is performed. A torque correction process (S8) correcting a torque value of the scroll compressor is performed by subtracting the unladen torque value from the laden torque value per angle during one rotation of a shaft obtained from the steps 4 and 7.