A position-of-magnetic-pole detecting device for detecting the position of a magnetic pole in a motor of a salient-pole type at the time of starting up the motor, comprising: a high-frequency voltage applying means (2, 8) configured for applying a d-axis high-frequency voltage comprising a sinusoidal harmonic and a null q-axis voltage to said motor, wherein the d-axis voltage is varied within one cycle of 360° at a predetermined rate at predetermined intervals; a driving current detecting means configured for detecting a feed back current of a driving current, which flows through said motor, after said high-frequency voltage applying means applies the high-frequency voltage while an excitation phase is being changed; a means configured for calculating the product of a derivative of the feed back current of a driving current, which is detected by said driving current detecting means, by the high-frequency voltage; a filter means configured for removing a high-frequency component from the product of the derivative of the feed back current of a driving current by the high-frequency voltage; a direction-of-magnetic-pole detecting means configured for detecting the direction of a magnetic pole by acquiring, from an output of said filter means, a peak value assumed by the product of the derivative of the feed back current of a driving current by the high-frequency voltage; a rectangular-wave voltage applying means configured for driving said motor by applying positive and negative rectangular-wave voltages, which have a magnitude causing magnetic saturation, with the excitation phase fixed to the direction of a magnetic pole detected by said direction-of-magnetic-pole detecting means; a peak current detecting means configured for detecting the peak values of the feed back currents of driving currents returned when the positive and negative rectangular-wave voltages are applied in order to drive said motor; and a polarity-of-magnetic-pole acquiring means configured for detecting the polarity of a magnetic pole according to the values of the feed back currents of positive and negative driving currents. a high-frequency voltage applying means (2, 8) configured for applying a d-axis high-frequency voltage comprising a sinusoidal harmonic and a null q-axis voltage to said motor, wherein the d-axis voltage is varied within one cycle of 360° at a predetermined rate at predetermined intervals; a driving current detecting means configured for detecting a feed back current of a driving current, which flows through said motor, after said high-frequency voltage applying means applies the high-frequency voltage while an excitation phase is being changed; a means configured for calculating the product of a derivative of the feed back current of a driving current, which is detected by said driving current detecting means, by the high-frequency voltage; a filter means configured for removing a high-frequency component from the product of the derivative of the feed back current of a driving current by the high-frequency voltage; a direction-of-magnetic-pole detecting means configured for detecting the direction of a magnetic pole by acquiring, from an output of said filter means, a peak value assumed by the product of the derivative of the feed back current of a driving current by the high-frequency voltage; a rectangular-wave voltage applying means configured for driving said motor by applying positive and negative rectangular-wave voltages, which have a magnitude causing magnetic saturation, with the excitation phase fixed to the direction of a magnetic pole detected by said direction-of-magnetic-pole detecting means; a peak current detecting means configured for detecting the peak values of the feed back currents of driving currents returned when the positive and negative rectangular-wave voltages are applied in order to drive said motor; and a polarity-of-magnetic-pole acquiring means configured for detecting the polarity of a magnetic pole according to the values of the feed back currents of positive and negative driving currents.