Disclosed is a visible light responsive photocatalyst that simultaneously realizes high crystallinity and refinement of primary particles. Also disclosed is a photocatalyst composed of secondary particles that have a high porosity and are aggregates of fine primary particles. Rhodium-doped strontium titanate that is a visible light responsive photocatalyst of the present invention has a primary particle diameter of not more than 70 nm and has a absorbance at a wavelength of 570 nm of not less than 0.6 and a absorbance at a wavelength of 1800 nm of not more than 0.7, each absorbance determining by measuring a diffuse reflection spectrum, the rhodium-doped strontium titanate having a high water-splitting activity as a photocatalyst.