A current leading-in method in a position sensor-less control system of an AC synchronous electric motor has an out-of-step problem. A high-frequency voltage component from a single-phase high-frequency voltage generating unit is transformed in coordinates by a high-frequency voltage coordinate transforming unit, and the transformed high-frequency voltage and a voltage command from a current control unit are synthesized to a voltage command value, which is outputted to an inversely rotational coordinate transforming unit. From the two-axis current components detected, a single-phase axial-phase signal is detected to generate a phase signal of a high-frequency voltage. This phase signal is used as the phase signal at the coordinate transformation time, and is outputted to a stabilization frequency correcting unit, thereby to calculate a correction signal. This correction signal and a frequency command are added to make the reference phase signal.