In a calculation for estimating axis error in a permanent magnet motor, a d-axis commanded voltage value is added to the product of three signals, which are a q-axis detected current value or commanded current value, an inductance value, and an estimated speed value, and then the resulting value is divided by the product of a commanded speed value ωr* and induced voltage constant Ke* or an arctangent calculation is performed in the same way, instead of using a resistance setting.