A photodiode includes a silicon semiconductor layer; a P-type high concentration diffusion layer with a P-type impurity diffused therein at a high concentration; an N-type high concentration diffusion layer with an N-type impurity diffused therein at a high concentration; and a low concentration diffusion layer with one of the P-type impurity and the N-type impurity diffused therein at a low concentration. The P-type high concentration diffusion layer and the N-type high concentration diffusion layer are formed in the silicon semiconductor layer, and are arranged to face each other with the low concentration diffusion layer in between. The photodiode further includes an interlayer insulation film formed on the silicon semiconductor layer, so that a covalent bond between silicon and hydrogen is formed in an atom row of the low concentration layer adjacent to an interface thereof with respect to the interlayer insulation film. The silicon semiconductor layer where the low concentration layer is formed may have a thickness between 3 nm and 36 nm.