An electric rotating machine has a rotor, a stator and a casing. A planetary roller mechanism constituted by a sun roller, a planet roller, a ring roller and a carrier is provided within the rotor so as to transmit the driving force of the rotor to the outside from a power shaft. Oil is sealed within the rotor or the casing. The planetary roller mechanism may be provided within the casing or at the outside of the rotor and, in this case, oil is sealed within the casing.