In an apparatus for controlling a rotary electric machine, a voltage applier applies a high-frequency voltage to one of the field winding and the armature winding. One of a field winding and an armature winding is defined as an input winding, and the other thereof is defined as an output winding. A current detector detects a high-frequency current flowing through the output winding based on the applied high-frequency voltage. The high-frequency current includes therein information associated with the rotational position of a target magnetic pole of the rotor as a predetermined one of the magnetic poles. An estimator estimates the rotational position of the target magnetic pole of the rotor according to the high-frequency current detected by the current detector.