Abstract: A lower cladding layer is laminated on a substrate and constituted of at least one layer. A light absorption layer is laminated on the lower cladding layer. An upper cladding layer is laminated above the light absorption layer and constituted of at least one layer. A light incident end surface is provided on at least one of the substrate and the lower cladding layer, and, when a light is made incident at a predetermined angle, enables the light to be absorbed in the light absorption layer and to be output as a current. An equivalent refractive index of the at least one of the substrate and the lower cladding layer is larger than that of the upper cladding layer. The predetermined angle is an angle enabling a light incident into the light absorption layer to be reflected at a lower surface of the upper cladding layer.