PURPOSE: To cool a resistance material and dissipate its heat effectively by forming, in a ventilation barrel, a space part defined between a plurality of stators, and between rotor cores, and by a machine frame, and by causing a blowing apparatus to communicate with a blower port or exhaust port opened in said machine frame.

CONSTITUTION: Rotor cores 2, 3 are fitted to a rotor shaft 4 and a non-magnetic material core is interposed between said rotor cores 2, 3. Respective conductors 5 furnished at said rotor cores 2, 3 are connected in series and both ends thereof are connected by short-circuit rings 6, 7. Also, the rotor cores 2, 3 and non-magnetic material cores are provided with a plurality of ventilation barrels for connecting the rotor cores 2, 3 and non-magnetic cores with both ends 10, 11 of a rotor 8. A space part 66 defined between said rotor cores 2, 3, and by a turning stator 31 fitted to a sliding bearing 26, by a second stator 25 fixed at a ventilation fixing ring 27A and a stator ring 27B, and by a machine frame 14 is formed in a ventilation barrel 67. A blower port 68 is opened in one side part of said machine frame 14 to communicate with said ventilation barrel 67, and an exhaust port 69 is opened in the machine frame 14 facing the blower port 68. A blowing apparatus 73 is immovably provided in the machine frame 14.