A visible light responsive photocatalyst powder having organic gas decomposition performance, wherein: (a) the visible light responsive photocatalyst powder comprises a tungsten oxide powder or a tungsten oxide composite material powder, and the tungsten oxide powder or the tungsten oxide composite material powder constituting the visible light responsive photocatalyst powder has a BET specific surface area in a range of not less than 4.1 m 2 /g nor more than 820 m 2 /g, (b) the tungsten oxide that forms the tungsten oxide powder or the tungsten oxide composite material powder has a crystal structure in which a rhombic crystal, a monoclinic crystal and a triclinic crystal of tungsten trioxide are mixed, (c) the organic gas decomposition performance of the visible light responsive photocatalyst powder responds nonlinearly to an amount of irradiated light under visible light in an illuminance range of not less than 200 lx nor more than 2500 lx, (d) the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 2500 lx is irradiated by using a white fluorescent lamp and an ultraviolet cutoff filter is 20% or more, the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 1000 lx is irradiated is 15% or more, the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 600 lx is irradiated is 10% or more, and the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 200 lx is irradiated is 5% or more, the acetaldehyde gas decomposition rate (%) being set as a value calculated based on [formula: (A - B) / A × 100], where A represents a gas concentration before light irradiation and B represents a gas concentration when not less than 15 minutes have elapsed from the light irradiation and, at the same time, the gas concentration is stable, the gas concentrations being measured while allowing an acetaldehyde gas having an initial concentration of 10 ppm to flow, at 140 mL/min, into a flow-type apparatus as is used in the evaluation of nitrogen oxide removal performance (decomposition performance) of JIS-R-1701-1 in which 0.2 g of a sample is placed, and (e) the tungsten oxide composite material powder contains at least one metal element selected from Ti, Fe, Cu, Zr, Ag, Pt, Pd, Mn, Al and Ce in a range of 50 mass% or less. (a) the visible light responsive photocatalyst powder comprises a tungsten oxide powder or a tungsten oxide composite material powder, and the tungsten oxide powder or the tungsten oxide composite material powder constituting the visible light responsive photocatalyst powder has a BET specific surface area in a range of not less than 4.1 m 2 /g nor more than 820 m 2 /g, (b) the tungsten oxide that forms the tungsten oxide powder or the tungsten oxide composite material powder has a crystal structure in which a rhombic crystal, a monoclinic crystal and a triclinic crystal of tungsten trioxide are mixed, (c) the organic gas decomposition performance of the visible light responsive photocatalyst powder responds nonlinearly to an amount of irradiated light under visible light in an illuminance range of not less than 200 lx nor more than 2500 lx, (d) the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 2500 lx is irradiated by using a white fluorescent lamp and an ultraviolet cutoff filter is 20% or more, the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 1000 lx is irradiated is 15% or more, the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 600 lx is irradiated is 10% or more, and the acetaldehyde gas decomposition rate when visible light having only a wavelength of not less than 380 nm and an illuminance of 200 lx is irradiated is 5% or more, the acetaldehyde gas decomposition rate (%) being set as a value calculated based on [formula: (A - B) / A × 100], where A represents a gas concentration before light irradiation and B represents a gas concentration when not less than 15 minutes have elapsed from the light irradiation and, at the same time, the gas concentration is stable, the gas concentrations being measured while allowing an acetaldehyde gas having an initial concentration of 10 ppm to flow, at 140 mL/min, into a flow-type apparatus as is used in the evaluation of nitrogen oxide removal performance (decomposition performance) of JIS-R-1701-1 in which 0.2 g of a sample is placed, and (e) the tungsten oxide composite material powder contains at least one metal element selected from Ti, Fe, Cu, Zr, Ag, Pt, Pd, Mn, Al and Ce in a range of 50 mass% or less.