In a solid-state imaging element, reflecting layers are provided on both sides of a photoelectric conversion means, a light entrance window 128 is provided in the first reflecting layer 121 disposed on the photon incidence side, and a concentration means 122 is provided at a position corresponding to the window. Further, a transparent layer 136 is provided between the photoelectric conversion means and a second reflecting layer 120. A structure where photons that entered between the two reflecting layers do not flow outside is preferably employed as the shape of the second reflecting layer 120. According to the present invention, detection sensitivity of a solid-state imaging element and a photo-detector using the same is improved, and a personal authentication system carrying a photo-detector showing improved detection sensitivity is provided.