To prevent the durability of a heater and a circuit board from being deteriorated by the peeling of an electrode, oxidization, deposition of crystals which are caused in a high-temperature and oxidizing atmosphere such as in a photographic processing device.

An electrode layer formed at the end of a ceramic heating element is coated with a heat resistant and acidproof protective layer of a silicone resin. In addition, required portions of the circuit board are coated with a silicone resin layer.