An automotive hybrid engine assist system characterized in comprising: a generator-motor that is coupled to an internal combustion engine of an automotive vehicle so as to act as a motor to assist said internal combustion engine or so as to be driven by said internal combustion engine to generate three-phase alternating-current power during idling standby; a battery that constitutes a power source for a direct-current load and for starting; a turbocharger comprising: a compressor that is disposed in an induction system of said internal combustion engine, and that compresses intake gas; a turbine that is mounted coaxially onto a rotating shaft of said compressor, and that is disposed in an exhaust system of said internal combustion engine; and a rotary machine that is mounted coaxially onto said rotating shaft; an inverter that is connected by means of wiring to three-phase power terminals of said generator-motor and three-phase power terminals of said rotary machine, and that converts direct-current power from said battery into three-phase alternating-current power and supplies said three-phase alternating-current power to said generator-motor when connected to said generator-motor, and that converts direct-current power from said battery into three-phase alternating-current power and supplies said three-phase alternating-current power to said rotary machine when connected to said rotary machine; a rectifying circuit that is constituted by a three-phase diode bridge, that is connected in parallel to said inverter between said three-phase power terminals of said generator-motor and said battery, and that converts said three-phase alternating-current power that is generated by said generator-motor into direct-current power and supplies said direct-current power to said battery; and an electric power direction change-over switch that is disposed in a path of said wiring, and that switches connection of said inverter to said generator-motor or to said rotary machine. a generator-motor that is coupled to an internal combustion engine of an automotive vehicle so as to act as a motor to assist said internal combustion engine or so as to be driven by said internal combustion engine to generate three-phase alternating-current power during idling standby; a battery that constitutes a power source for a direct-current load and for starting; a turbocharger comprising: a compressor that is disposed in an induction system of said internal combustion engine, and that compresses intake gas; a turbine that is mounted coaxially onto a rotating shaft of said compressor, and that is disposed in an exhaust system of said internal combustion engine; and a rotary machine that is mounted coaxially onto said rotating shaft; an inverter that is connected by means of wiring to three-phase power terminals of said generator-motor and three-phase power terminals of said rotary machine, and that converts direct-current power from said battery into three-phase alternating-current power and supplies said three-phase alternating-current power to said generator-motor when connected to said generator-motor, and that converts direct-current power from said battery into three-phase alternating-current power and supplies said three-phase alternating-current power to said rotary machine when connected to said rotary machine; a rectifying circuit that is constituted by a three-phase diode bridge, that is connected in parallel to said inverter between said three-phase power terminals of said generator-motor and said battery, and that converts said three-phase alternating-current power that is generated by said generator-motor into direct-current power and supplies said direct-current power to said battery; and an electric power direction change-over switch that is disposed in a path of said wiring, and that switches connection of said inverter to said generator-motor or to said rotary machine. a compressor that is disposed in an induction system of said internal combustion engine, and that compresses intake gas; a turbine that is mounted coaxially onto a rotating shaft of said compressor, and that is disposed in an exhaust system of said internal combustion engine; and a rotary machine that is mounted coaxially onto said rotating shaft; an inverter that is connected by means of wiring to three-phase power terminals of said generator-motor and three-phase power terminals of said rotary machine, and that converts direct-current power from said battery into three-phase alternating-current power and supplies said three-phase alternating-current power to said generator-motor when connected to said generator-motor, and that converts direct-current power from said battery into three-phase alternating-current power and supplies said three-phase alternating-current power to said rotary machine when connected to said rotary machine; a rectifying circuit that is constituted by a three-phase diode bridge, that is connected in parallel to said inverter between said three-phase power terminals of said generator-motor and said battery, and that converts said three-phase alternating-current power that is generated by said generator-motor into direct-current power and supplies said direct-current power to said battery; and an electric power direction change-over switch that is disposed in a path of said wiring, and that switches connection of said inverter to said generator-motor or to said rotary machine.