An apparatus is provided for controlling a synchronous motor. The apparatus comprises a first calculator calculating a voltage characteristic showing a characteristic of voltages to be applied to armature coils of a stator and a producer producing a command signal to provide the armature coils with the phase currents on the basis of the voltage characteristic. The apparatus still comprises a current detector detecting a signal depending on an amplitude of at least one of the phase currents, a second calculator calculating a rate of changes in a current amount indicating amplitudes of the phase currents, by using the signal from the current detector, and a feed-back member feed-backing the rate of changes in the current amount into the calculation of the voltage characteristic.