A magnetic pole position detector includes, a voltage command unit that generates high-frequency voltage command in a dq coordinate system, a three-phase transformation unit that transforms the high-frequency voltage command in the dq coordinate system to high-frequency voltage command in a three-phase coordinate system by using an estimated magnetic pole position, a current detection unit that detects three-phase current fed from a power converter for generating drive power, a dq transformation unit that transforms the detected three-phase current to current in the dq coordinate system by using the estimated magnetic pole position, an estimated magnetic pole position calculation unit that calculates a new estimated magnetic pole position to be used in three-phase dq transformations, and a magnetic pole position confirmation unit that confirms that, when converging on a certain position, the estimated magnetic pole position is the magnetic pole position at the time when the synchronous motor is started.