To provide an exhaust gas heat recovering device capable of retaining a fuel-air ratio of a reheating burner substantially constantly irrespective of the presence or absence of supplying the gas.

The exhaust gas heat recovering device using an exhaust gas heat of an engine as a heat source comprises a furnace body 52 provided at an exhaust gas channel 5 for distributing an exhaust gas from the engine, a reheating burner means 51 provided in the body 52 to burn a fuel, and an air supply means 58 provided in the body 52 to supply combustion air. The device further comprises a control means for controlling a fuel from rate of the means 51 and/or a supply flow rate of the air to the body 52 and to control the means 51 and/or the means 58 so that a fuel/air ratio of the fuel to the combustion air becomes substantially constant even when a flowing amount of the exhaust gas into the body 51 is changed.