Waste heat from an engine is effectively converted into power and the power is stored in a dedicated power storage device to freely output boost pressure from an electric air compressor so as to improve fuel efficiency, drivability, and exhaust gas purification. The present invention comprises: a steam cycle device (2) which rotates an expander (25) by expanding steam generated by waste heat from an engine (1); a first power generator (5) which is connected to the expander (25) and generates power using torque from the expander (25); a dedicated battery (8) which stores the power that is generated by the first power generator (5); and an electric supercharger (9) which drives a first compressor (11) using a motor (14) driven by the power in the dedicated battery(8) and generates compressed air.