To provide a heat exchange device preventing the corrosion of an exhaust passage caused by acid condensed water in advance by preventing the dew condensation of the exhaust, though the heat exchange device can obtain high heat exchanging efficiency by comprising a heat exchanger for collecting latent heat, and securing high safety when it is installed as an indoor device.

An exhaust extension passage 17 for discharging the exhaust after heat exchanging is installed from a downstream side of the exhaust passage with respect to a secondary heat exchanger 50 to the external opened to the outside air, and a bypass passage 32 is formed in a state of being branched from an air supply passage for supplying the air to the fuel, and communicated and connected to a starting end side of the exhaust extension passage 17 at its branched part, for guiding the air to dilute the exhaust in the exhaust extension passage 17.