To enhance heat utilizing efficiency as a whole, by making maximum use of heat included in exhaust gas by utilizing not only combustion exhaust gas of an internal combustion engine but also low temperature exhaust heat by combination.

Middle temperature combustion exhaust gas accompanied with mixture explosion of fuel F and air A is supplied to an superheating part 2C of a boiler 2 to generate a medium pressure superheat steam, and the thus generated steam in the boiler 2 is supplied through a passage 11 to an intermediate pressure turbine 3 thereby driving the turbine, then, turbine exhaust is supplied to the superheating part 2C of the boiler 2 through a passage 12. A low pressure steam after cooling generated by water cooling by a cooling device including a cooling jacket 1B is introduced through a passage 13, and is supplied to the superheating part 2C of the boiler 2 together with the turbine exhaust. By a low pressure superheat steam from the superheating part 2C, a low pressure turbine 4 is driven through a passage 14, a generator 5 is driven, the turbine exhaust is introduced to a condenser 6, and the condensed water in the condenser is supplied through a return passage 17 to a preheat part 2a of the boiler 2 by means of a supply pump 7. Further, a part of the condensate from the condenser 6 is supplied through a return passage 18 to the cooling jacket 1B by means of the supply pump 7.