PURPOSE: To precisely and easily carry out troublesome setting of motor constant by identifying secondary resistance by way of using secondary circuit time constant of phase difference of zero and magnetization inductance of amplitude difference of zero.

CONSTITUTION: A magnetic flux computing part 116 is changed over to three constitutions of tuning of phase discrimination, secondary circuit time constant and magnetization inductance. At the time of phase discrimination, phase and direction are found in relation with a speed controller 101, a sinusoidal wave generator 121 and a two phase/three phase converter 106. Thereafter, in a tuning mode of the secondary circuit time constant, as two outputs of the sinusoidal wave generator 121, sinusoidal wave of 90 degrees phase difference of Sin wave and Cos wave is generated. Thereafter, inverse value of the secondary circuit time constant is measured by an internal mechanism of the magnetic flux computing part 116. At last, in a tuning mode of the magnetization inductance, the Sin wave from the sinusoidal wave generator 121 is input to the internal mechanism of the magnetic flux computing part 116. Thereby, the magnetization inductance is measured, and from a coefficient multiplier, secondary resistance is found.