Provided are a photocatalyst which is high in catalytic activity, is nontoxic, has a long life, allows visible light to be used directly for its photocatalytic reaction and is especially useful for hydrogen generation, and a process for producing it. It contains a cadmium compound, has a capsular structure, has an average particle diameter of 100 nm or less and can be manufactured by dropping a solution of a cadmium salt into a solution of a sodium compound or admixing a solution of a sodium compound in a suspension of particles of a cadmium compound.