In one embodiment, a visible light responsive photocatalyst powder has organic gas decomposition performance that 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. The visible light responsive photocatalyst powder has a gas decomposition rate of 20% or more, for example, when visible light having only a wavelength of not less than 380 nm and an illuminance of 2500 lx is irradiated, the 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 into a flow-type apparatus in which 0.2 g of a sample is placed.