To obtain a heater, in which the heating capacity is prevented from lowering due to the assembling accuracy of a heat exchanger, while ensuring proper cleaning performance.

Fins 12, each having a bend at one end and fixed in heat exchanging relation with a heating medium tube, and a radiation plate 14 fixed in heat exchanging relation with the fins 12 by resiliency of the bend 13, are provided. An air conditioner, having superior cleaning performance, can be realized because the radiati plate 14 has no joint. Since the fin touches the radiation plate through the resiliency of the bend 13, air will not leak from the joint of the fins, even if the assembling accuracy of the fins is low, and since thermal expansion of the fin is absorbed by resiliency of the bend, radiant quantities or heating capacity will not be lowered, even if the fins has a high temperature resulting in high efficiency heating.