A photodiode formed over a silicon substrate is disclosed. The photodiode includes a light-receiving region formed of a diffusion region of a first conduction type at the surface of the silicon substrate and forming a pn junction; an intermediate region formed of a diffusion region of the first conduction type at the surface of the silicon substrate so as to be included in the light-receiving region; a contact region formed of a diffusion region of the first conduction type at the surface of the silicon substrate so as to be included in the intermediate region; a shield layer formed of a diffusion region of a second conduction type in a part of the surface of the silicon substrate outside the intermediate region; and an electrode in contact with the contact region. The shield layer faces the side end part of the diffusion region forming the intermediate region.