A thermoelectric generator (13) has a module chamber (32) defined between an exhaust pipe portion (19) and a coolant pipe (23). A thermoelectric conversion module (22) and an HC sensor (35) are located in the module chamber (32). An ECU performs a fault diagnosis on the thermoelectric generator (13) by detecting the leakage of exhaust gas into the module chamber (32) from the exhaust pipe portion (19) based on detection information output by the HC sensor (35).