A magnetic pole position estimation device for a synchronous motor, comprising: voltage applying means for applying a voltage to each of phases of a synchronous motor based on a voltage command; current detecting means for detecting a current flowing through the each of the phases of the synchronous motor according to the applied voltage; storing means for storing a plurality of voltage command vectors having the same amplitude with phase differences obtained by equally dividing 360 degrees; voltage controlling means for causing the voltage applying means to sequentially switch and apply a plurality of pulse voltages for magnetic pole position estimation to the each of the phases of the synchronous motor based on the voltage commands obtained by transforming the plurality of voltage command vectors; estimating means for calculating a plurality of current vectors based on an amplitude of the current, and for estimating an initial magnetic pole position of a rotor of the synchronous motor based on a phase of a mean vector obtained by averaging the plurality of current vectors corresponding to the plurality of voltage command vectors, respectively; characterized in that the estimating means is for calculating the plurality of current vectors based on the amplitude of the current flowing through the each of the phases of the synchronous motor in synchronization with the plurality of pulse voltages for magnetic pole position estimation, and for estimating an initial magnetic pole position of a rotor of the synchronous motor based on a phase of a mean vector obtained by averaging two-phase transforms of the plurality of current vectors corresponding to the plurality of voltage command vectors, respectively; and in that the magnetic pole position estimation device comprises: estimate correctness judging means for judging whether the initial magnetic pole position estimated by the estimating means is correct or incorrect based on a magnetic saturation judgment current value based on the current values detected by the current detecting means and a predetermined magnetic saturation current threshold; current threshold storing means for storing the predetermined magnetic saturation current threshold; and pulse voltage application condition changing means for changing, when the estimate correctness judging means judges that the initial magnetic pole position estimated by the estimating means is incorrect, an application condition on the pulse voltage so that desired magnetic saturation occurs. voltage applying means for applying a voltage to each of phases of a synchronous motor based on a voltage command; current detecting means for detecting a current flowing through the each of the phases of the synchronous motor according to the applied voltage; storing means for storing a plurality of voltage command vectors having the same amplitude with phase differences obtained by equally dividing 360 degrees; voltage controlling means for causing the voltage applying means to sequentially switch and apply a plurality of pulse voltages for magnetic pole position estimation to the each of the phases of the synchronous motor based on the voltage commands obtained by transforming the plurality of voltage command vectors; estimating means for calculating a plurality of current vectors based on an amplitude of the current, and for estimating an initial magnetic pole position of a rotor of the synchronous motor based on a phase of a mean vector obtained by averaging the plurality of current vectors corresponding to the plurality of voltage command vectors, respectively; characterized in that the estimating means is for calculating the plurality of current vectors based on the amplitude of the current flowing through the each of the phases of the synchronous motor in synchronization with the plurality of pulse voltages for magnetic pole position estimation, and for estimating an initial magnetic pole position of a rotor of the synchronous motor based on a phase of a mean vector obtained by averaging two-phase transforms of the plurality of current vectors corresponding to the plurality of voltage command vectors, respectively; and in that the magnetic pole position estimation device comprises: estimate correctness judging means for judging whether the initial magnetic pole position estimated by the estimating means is correct or incorrect based on a magnetic saturation judgment current value based on the current values detected by the current detecting means and a predetermined magnetic saturation current threshold; current threshold storing means for storing the predetermined magnetic saturation current threshold; and pulse voltage application condition changing means for changing, when the estimate correctness judging means judges that the initial magnetic pole position estimated by the estimating means is incorrect, an application condition on the pulse voltage so that desired magnetic saturation occurs. estimate correctness judging means for judging whether the initial magnetic pole position estimated by the estimating means is correct or incorrect based on a magnetic saturation judgment current value based on the current values detected by the current detecting means and a predetermined magnetic saturation current threshold; current threshold storing means for storing the predetermined magnetic saturation current threshold; and pulse voltage application condition changing means for changing, when the estimate correctness judging means judges that the initial magnetic pole position estimated by the estimating means is incorrect, an application condition on the pulse voltage so that desired magnetic saturation occurs.