<p>A cogeneration apparatus (10; 110) includes: an airtight chamber (12) provided within an apparatus casing (11) and constructed to prevent exhaust gas of a prime mover (14) from flowing out therefrom; and a relief valve (93; 113) provided in a water flow path (85) within the airtight chamber (12) and constructed to discharge the exhaust gas, contained in the water flow path, to the airtight chamber.</p>
