NOVELTY - The electrically-driven supercharger (9) has a vapor-cycle apparatus (2) that rotates a steam turbine (25) with the vapor generated with the heat of the waste gas discharged from an engine (1). A battery stores the electric power generated by electric power generating apparatus (3). A motor (14) is driven with the electric power of battery and provided to drive a compressor (11) to generate compressed air. The battery electrically stores only the electric power for driving the electrically-driven supercharger.    USE - Electrically-driven supercharger for use in internal combustion engine of vehicle.    ADVANTAGE - By driving the compressor the generation of compressed air can respond according to the driving state of the vehicle without using the electric power to supply the existing electrical component of the vehicle. The waste heat from the engine can be converted effectively into power. The power can be stored in the dedicated power storage device so as to freely output air supply pressure from the electric air compressor. The fuel efficiency, drivability and exhaust gas purification of the supercharger can be improved. The ambient temperature of the supercharger can be reduced and high heat resistance is not required for the motor inverter so that operating cost of the supercharger can be reduced. The occurrence of the increase in engine pressure emission can be suppressed. By producing electric power with the vapor-cycle apparatus, the energy-recovery efficiency of the supercharger can be improved. The number of components of the converter and generator can be reduced so that the manufacturing cost of the supercharger can be reduced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an electric power supply method.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the structure of the electrically-driven supercharger. (Drawing includes non-English language text)    Engine (1)    Vapor-cycle apparatus (2)    Electric power generating apparatus (3)    Electrically-driven supercharger (9)    Compressor (11)    Motor (14)    Steam turbine (25)