To restrain the clogging of an exhaust pipe and a sulfuric acid corrosion by the lowering of an exhaust gas temperature, in a heating system by which the exhaust heat of an engine is utilized as a heat source.

A heat pump A driven by an engine 1 has a refrigerant heater 6 for recovering an engine exhaust heat from a cooling water circuit W of the engine 1 and for heating refrigerant. A filter 8 for gathering a soot and a combustion burner 9 for reproduing the filter are provided in the exhaust gas passage P of the engine 1 and one part of the cooling water circuit W is arranged around the filter 8 and the heat recovering unit 10 is constituted and a solenoid valve 11 for opening/closing a cooling water flow passage to the heat recovering unit 10 is provided. Only at the shortage time of the heating capability of the heat pump A, the combustion burner 9 is started and the solenoid valve 11 is opened and the heat from the heat recovering unit 10 is sent to a refrigerant heater 6 and is utilized as a heat source.