Abstract: An induction machine used as a power generator for an internal combustion engine, and which generates a predetermined power regardless of a rotation speed of a rotor of the induction machine and the engine. A power P to be generated is controlled so as to be equal to an upper limit value Pmax or less, a lower limit value or more or, equal to a target value Pc. The power generation control is achieved in the following manner. A speed N2 of the rotating magnetic field electrically generated with a three-phase winding of the rotor 1R is controlled in accordance with the mechanical rotation speed N1 of the rotor 1R in order that a relative speed N of the rotating magnetic field generated in the rotor with respect to a stator coil is kept at an upper limit speed Nmax or less, a lower limit speed Nmin or more, or a target relative speed Nc.