A photocatalyst device including: a body; a light source part fixed to the body to irradiate ultraviolet light and having an LED and a substrate for fixing the LED thereto; a catalyst part fixed to the body to conduct photocatalytic reaction with the light irradiated by the light source part and thus to generate superoxygen radicals; and a heat radiating part disposed on the light source part to radiate the heat generated from the light source part, whereby the photocatalyst device purifies air and sterilizes and deodorizes the evaporator, while being easily mountable as a single module.