To silence the combustion sound, covering wide frequency band, by equipping a silencer with an exhaust path leading to an exhaust port from a combustion chamber, and providing a plurality of silencing chambers within the exhaust path.

An operation switch is turned on, and a hot water supply plug, etc., are opened, and when the flow rate comes to a certain flow rate, and a blower 1 supplies a combustion chamber 2 with air for combustion to start the combustion. Then, the air after combustion is exhausted out of a combustor through an exhaust chamber 3 being a first silencing chamber, an exhaust cylinder 4 being a second silencing chamber, and an exhaust port 5 provided within an exhaust path. Hereby, the exhaust chamber 3 muffles the combustion sound of high frequency band and the exhaust cylinder 4 muffles the combustion sound of low frequency band, so this silencer can silence the combustion sound, covering wide frequency band.