To facilitate a method for function recovery and enhancement of adsorption performance of a photocatalyst or the like attaining decomposition and regeneration of a harmful substance for regenerating the harmful substance adsorbed after adsorbing/removing the harmful gas and bad odor gas components in an atmosphere utilizing light energy of UV rays or the like.

The photocatalyst filter comprises a diffusion film (1) for effectively irradiating the photocatalyst processed to a flat surface or a pleat-like shape comprising various kinds of resin material of PET, PC or the like wound to a helical shape or a concentric circle-like shape with the light energy, a filter material (2) in which a fibrous material or the like is carried with the photocatalyst similarly wound in the helical shape, a light source part (4) for feeding the light energy of UV rays or the like for regenerating function of the photocatalyst, and a box body 3 made of a resin or steel plate for retaining them.