A hybrid vehicle has a transmission coupled to the output shaft of an engine for transmitting an output power of the engine to drive wheels of the hybrid vehicle. A generator motor is coupled to the transmission for transmitting an assistive output power for assisting the output power of the engine through the transmission to the drive wheels. A battery stores electric energy regenerated by the generator motor, operating as an electric motor, from kinetic energy of the hybrid vehicle transmitted from the drive wheels through the transmission when the hybrid vehicle is decelerated. A transmission control unit establishes a speed reduction ratio for the transmission to achieve a predetermined regeneration efficiency for the generator motor when the hybrid vehicle is decelerated, and controls the transmission at the established speed reduction ratio.