Abstract: An exhaust case having the first exhaust gas flow path for flowing combustion exhaust gas passing upward through a heat exchange, behind a water-shielding plate and for guiding the combustion exhaust gas onto the water-shielding plate toward an exhaust vent, and having the second exhaust gas flow path for flowing a part of combustion exhaust gas into a space between the water-shielding plate and a horizontal plate part and further into the exhaust vent. A ventilation hole is provided for an upright plate part extending from the rear end of the horizontal plate part in order to flow combustion exhaust gas into the space, and is provided in the substantially horizontal direction. Accordingly, the exhaust case is inhibited to become large scaled, and a superior exhaust noise-reduction effect, a suppression effect of combustion oscillation of the burner, and a waterproof performance are able to be achieved.