PROBLEM TO BE SOLVED: To improve the photocatalytic activity by depositing a noble metal on photocatalytic active points or near the points. SOLUTION: A metal promoting photocatalytic activity in a solution of a salt of the metal is added to and mixed with a suspension solution of a photocatalytic particle and on the completion of the mixing or simultaneously with the mixing, ultraviolet rays are radiated to the mixed solution to generate electrons in the photoactive points of the photocatalyst particle and the added metal or its compound is reduced and precipitated on the photoactive points or near the points by the electrons.