A rotor position determination device for determining a position of a rotor of a rotating electric machine relative to m-phase (m is an integer equal to or more than 2) armature coils, the rotating electric machine including a stator having the m-phase armature coils, and the rotor having a magnetic field, includes: transient current energizing means for performing, for each of the m-phase armature coils, a transient current energizing process for temporarily applying a DC voltage to the armature coil of each phase of the rotating electric machine to pass a transient current through the armature coil of each phase; and rotor position determination means for detecting the transient current passed through each of the m-phase armature coils and determining the position of the rotor relative to the m-phase armature coils from the detected transient currents.