Light on the longer wavelength side can be photoelectrically converted and output reliably, whilst improving the structural and operational reliability of a photodetector, by means of a simple manufacturing process and inexpensive manufacturing costs. A first light-absorbing layer, a buffer layer of a second conductivity type, a second light-absorbing layer of a second conductivity type and a window layer of a second conductivity type are laminated in this order onto the first principal surface of a substrate of a first conductivity type. The first light-absorbing layer contains a region of the first conductivity type and a region of the second conductivity type, and a diffused region of the first conductivity type having a depth extending from the upper face of the window layer to the interface between the window layer and the second light-absorbing layer is provided in a portion of the window layer. A main electrode of a first conductivity type is provided on the diffused region, whilst a main electrode of a second conductivity type is provided on the window layer in the vicinity of the diffused region. The energy gap wavelength of the second light-absorbing layer is longer than the energy gap wavelength of the first light-absorbing layer, whilst the energy gap wavelength of the first light-absorbing layer is longer than the respective energy gap wavelengths of the substrate, buffer layer and window layer.