A reference current phase sensing part of a sensor phase (W) calculates an α-axis current iα and a β-axis current iβ in a fixed coordinate system formed with respect to a sensor phase as a base. The α-axis current iα is calculated based on a sensed current iw.sns of the sensor phase and a β-axis current iβ is calculated based on command currents iu* and iv* of the other two phases (U, V) determined from a d-axis command current id* and a q-axis command current iq*. Then a current phase xθ=tan−1(iβ/iα) is calculated. A basic wave estimating part calculates an estimated current iu.est of the other phase by calculating an estimation coefficient corresponding to the reference current phase xθ of the sensor phase and multiplying the sensed current iw.sns of the sensor phase by the estimation coefficient.