To obtain a photodiode which is excellent in response characteristic by eliminating influence of background light injected to an outside of a photosensitive part of a photodiode.

A hole H by background light is trapped by a depletion layer Db formed by a background light trapping region 9 and does not contribute to light current by forming a p-type background light trapping region 9 in a circumference of a p-type photosensitive region 4 at intervals of at least a size L. Therefore, deterioration of response characteristic in not generated and fast speed is realized. Furthermore, in this structure, an equation of Nmin=2e/qL2.VBmin (wherein e is a dielectric constant of InP or InGaAs and q is charge elementary quantity) is required between a minimum distance L and a minimum value Nmin of carrier concentration of an N-InP window layer 3 or an n-InGaAs optical absorption layer 2 for realizing a breakdown strength of VBmin or more.