A pole direction detection device for detecting a pole direction of a synchronous motor having saliency comprises a high-frequency voltage application unit that applies a high-frequency voltage to the motor; an excitation phase change unit that changes an excitation phase of the motor to an arbitrary phase; a driving current detection unit that detects a driving current value of the motor; a pole direction estimation unit that detects a pole direction based on the excitation phase and the driving current value; a measurement unit that measures an inductance value of the motor; and a control unit that changes a frequency of the high-frequency voltage to be applied by the high-frequency voltage application unit based on the inductance value measured by the measurement unit.