A motor magnetic pole position detecting device includes a detection current command generation unit generating a detection AC current command, a current detection section detecting a current flowing into the motor, a coordinate conversion unit vector-converting the current detected by the current detection section into an excitation component and a torque component both represented by a d-q orthogonal coordinate system based on a phase angle obtained at any rotational frequency, a current control unit delivering a voltage command to current-control the motor based on the detection current command and the current converted by the coordinate conversion unit, an inductance calculation unit calculating motor inductance based on the voltage command and the current converted by the coordinate conversion unit, and a magnetic pole position detection section calculating a frequency and phase of the inductance calculated by the inductance calculation unit, converting the inductance phase into a motor magnetic pole position.