A photodiode array has a plurality of photodetector channels formed on an n-type substrate having an n-type semiconductor layer, with a light to be detected being incident to the photodetector channels. The array comprises: a p−-type semiconductor layer on the n-type semiconductor layer of the substrate; resistors is provided to each of the photodetector channels and is connected to a signal conductor at one end thereof; and an n-type separating part between the plurality of photodetector channels. The p−-type semiconductor layer forms a pn junction at the interface between the substrate, and comprises a plurality of multiplication regions for avalanche multiplication of carriers produced by the incidence of the light to be detected so that each of the multiplication regions corresponds to each of the photodetector channels.