An engine system includes a medium which chemically repeats storage and release of hydrogen to provide an engine system where CO2 emissions can be suppressed and system efficiency is excellent. The engine system includes a hydrogen supply device for producing hydrogen rich gas from a medium which chemically repeats the storage and release of hydrogen, and drives an engine using the hydrogen rich gas produced in the hydrogen supply device as one of the fuels. This engine system is characterized by comprising a waste heat supply device for supplying waste heat of the engine to hydrogen supply device, a generator which generates electricity by power of the engine, an energy storage device for storing electric power produced by the generator, and a motor for converting electric power discharged from the energy storage device into power.