An accessory drive system which is capable of preventing the driving efficiency thereof from being lowered and achieving simplified construction, and reduction of the size and manufacturing costs. The system has a rotating machine including a first rotor, a second rotor, and a stator. The first rotor is formed by magnetic poles circumferentially arranged, with each two adjacent ones having different polarities. The stator has an armature row for generating a rotating magnetic pole that circumferentially rotates, between the armature and magnetic pole rows. The second rotor is formed by soft magnetic material elements circumferentially arranged with space, and disposed between the magnetic pole and armature rows. A ratio between the number of the armature magnetic poles, that of the magnetic poles, and that of the soft magnetic material elements is set to 1:m:(1+m)/2(m≠1.0).