To reduce the fuel consumption per unit travel distance by automatically and gradually changing the vehicle speed range with its regenerative braking effective corresponding to the habits in driver's braking operation (habits due to the driver's character), even in such a case that the driver drives who does not necessarily execute drive operation as established as a standard in vehicle design.

When a deceleration operation regardless of an established deceleration pattern is repeated, the control logic of a program control circuit is gradually changed so that the vehicle speed range enabling the travelling energy to be effectively recovered by a battery is adapted to the drive operation, whenever such drive operation is repeated. Practically, a parameter controlling the rotary phase of a power generator is changed adaptively and automatically so as to increase the energy recovery efficiency in the vehicle speed range where the driver remarkably reduces speed.