An object is to improve fuel consumption, drivability and exhaust gas purification by efficiently converting waste heat of the engine into electrical power and storing the electrical power in a dedicated electric storage so that the boost pressure from the electric air compressor can be flexibly outputted. The electric supercharging device includes a steam cycle device configured to expand the steam generated by waste heat of an engine to rotate an expander, a first generator connected to the expander and configured to generate an electrical power by torque of the expander, a dedicated battery which stores the electrical power generated by the first generator, and an electric supercharger configured to drive a compressor with a motor driven by the electrical power of the dedicated battery to generate compressed air.