An automotive hybrid engine assist system that simultaneously mounts both an idling reduction system and an electric motor turbocharging system, and that is small, light, inexpensive, and fuel-efficient. Three-phase power terminals of a generator-motor and a super-high-speed rotary machine are respectively connected to an inverter by a large-current wiring. An electric power direction change-over switch is disposed in a path of the large-current wiring, and switches connection of the inverter to the generator-motor or to the super-high-speed rotary machine.