A method of estimating a rotational position of a motor having saliency, the method including the steps of a) superimposing, on a drive voltage for the motor, a measuring voltage having a predetermined frequency higher than a frequency of the drive voltage to generate three-phase voltages, and supplying the three-phase voltages to a stationary portion of the motor; b) in parallel with step a), extracting components of the predetermined frequency in three-phase currents flowing in the stationary portion as first, second, and third extracted currents; c) multiplying the first and second extracted currents together to acquire a first composite signal, multiplying the second and third extracted currents together to acquire a second composite signal, and multiplying the first and third extracted currents together to acquire a third composite signal; d) subjecting the first, second, and third composite signals to low-pass filtering to acquire first, second, and third filtered signals, respectively, the low-pass filtering passing low-frequency components including the frequency of the drive voltage; and e) acquiring a rotational position of the rotating portion based on the first, second, and third filtered signals.