With a thermo-siphon type heat exchanger including a heating section of and a heat transfer pipe of a thermoelectric power generation unit, the thermoelectric power generator recovers a heat from a hot gas flowing through a flow path and generates electricity. To the thermo-siphon type heat exchanger, a storage tank that stores a heat medium is connected in a communication state; transferring of the heat medium from the thermo-siphon type heat exchanger to the storage tank, and returning of the heat medium from the storage tank to the thermo-siphon type heat exchanger can adjust the heat medium amount in the thermo-siphon type heat exchanger. At least a part of the storage tank is placed in the flow path so that the stored heat medium is heated, and the stored heat medium can be cooled with a cooler that is capable of turning a cooling function ON/OFF.