To prevent ash dust from remaining between the middle temperature layer element and the low temperature layer element of an air preheater.

A gas inlet duct 2 is connected to the upper surface of a rotor housing 1 and a gas outlet duct 4 to the under surface thereof so that exhaust gas G from a boiler flows from above to below, and an air inlet duct 5 is connected to the under surface and an air outlet duct 3 to the upper surface so that air A flows from below toward above. A high temperature layer element 12, a middle temperature layer element 13, and a low temperature layer element 14 are disposed in the order from above toward below so that both exhaust gas G and air A flow. A nozzle pipe 26 through which a injection medium is injected toward the high temperature layer element 12 is disposed above the high temperature layer element 12 and a nozzle pipe 45 through which an injection medium is injected toward the low temperature layer element 14 is disposed between the middle temperature layer element 13 and the low temperature layer element 14.