An accessory drive system includes a stator, a first rotor, and a second rotor, which respectively include armatures, permanent magnets, and first and second cores. One of the first and second rotors is connected to an accessory, and the other to an internal combustion engine. When the polarity of a first armature magnetic pole is different from the polarity of a first magnetic pole of an opposed permanent magnet, the polarity of a second armature magnetic pole becomes the same as the polarity of a second magnetic pole of the opposed permanent magnet. When each first core is between the first magnetic pole and the first armature magnetic pole, each second core is between a pair of the second armature magnetic poles circumferentially adjacent to each other, and between a pair of the second magnetic poles circumferentially adjacent to each other.