An object of the invention is to provide a filter comprising a photocatalyst material having a higher catalyst effect than conventional photocatalyst materials.The photocatalyst material of the invention contains, as its major component, a tungsten oxide powder excited by a light source which emits light having a wavelength of 430 to 500 nm, the photocatalyst material having a decomposition ability of 50% or more wherein the decomposition ability is given by the following equation based on the following test:[Test for decomposition ability]1g of a tungsten oxide powder and 20 ppm of acetaldehyde (amount A) are poured into a 3-liter glass container, and acetaldehyde (amount B) is measured after light having a peak wavelength of 460 nm ± 10 nm is irradiated to the mixture for 2 hours to measure the decomposition ability (%):Decomposition ability (%) = [(acetaldehyde amount A - acetaldehyde amount B)/acetaldehyde amount A] × 100.
