A photodiode includes a photosensitive element formed in a silicon semiconductor layer on an insulation layer. The photosensitive element includes a low concentration diffusion layer, a P-type high concentration diffusion layer, and an N-type high concentration diffusion layer. A method of producing the photodiode includes the steps of: forming an insulation material layer on the silicon semiconductor layer after the P-type impurity and the N-type impurity are implanted into the low concentration diffusion layer, the P-type high concentration diffusion layer, and the N-type high concentration diffusion layer; forming an opening portion in the insulation material layer in an area for forming the low concentration diffusion layer; and etching the silicon semiconductor layer in the area for forming the low concentration diffusion layer so that a thickness of the silicon semiconductor layer is reduced to a specific level.