Photodiode with electrode for noise immunity

A photodiode comprising:

• a high-concentration first conductivity-type substrate;
• a low-concentration first conductivity-type epitaxial layer formed on one face of the substrate;
• a second conductivity-type diffusion layer formed in the epitaxial layer, the diffusion layer serving as a light-receptive section;
• a pair of electrodes comprising a cathode and an anode, one of the pair of electrodes being mounted on the second conductivity-type diffusion layer and the other being mounted on another face of the substrate or one of the pair of electrodes being mounted on the second conductivity-type diffusion layer and the other being mounted on the epitaxial layer except the diffusion layer;
• and
• a third electrode covering an outer periphery or an inner periphery of a region on four sides to pick up noise from all directions to the photodiode, the region being occupied by the second conductivity-type diffusion layer on the epitaxial layer, the third electrode not contacting the pair of electrodes.