PURPOSE: To recover exhaust heat efficiently thus to eliminate fire caused through crack in heatexchanger by providing a restriction mechanism in a path for forcefully circulating the heat medium oil of exhaust heat recovery heatexchanger thereby bringing the interior of the heatexchanger into negative pressure.

CONSTITUTION: An exhaust heat recovery heatexchanger 4 is inserted into an exhaust bypath 3 coupled to an exhaust path 2 from an engine 1. A path 6 for forcefully circulating the heat medium oil between the heatexchanger 4 and a thermal load unit 5 such as a hot water supply unit is provided. A mechanism 7 for restricting the flow path to bring the interior of the heatexchanger 4 into negative pressure is provided at the portion of the circulation path between the thermal load unit 5 and the heatexchanger 4. Said mechanism 7 will control the restriction on the basis of the outputs from units 8, 9 for detecting the inlet and the outlet pressures of the heatexchanger 4 to bring the interior of the heatexchanger 4 into negative pressure.