A photodiode array PDA1 is provided with a substrate S wherein a plurality of photodetecting channels CH have an n-type semiconductor layer 32. The photodiode array PDA1 is provided with a p− type semiconductor layer 33 formed on the n-type semiconductor layer 32, resistors 24 provided for the respective photodetecting channels CH and each having one end portion connected to a signal conducting wire 23, and an n-type separating portion 40 formed between the plurality of photodetecting channels CH. The p− type semiconductor layer 33 forms pn junctions at an interface to the n-type semiconductor layer 32 and has a plurality of multiplication regions AM for avalanche multiplication of carriers generated with incidence of detection target light, corresponding to the respective photodetecting channels. An irregular asperity 10 is formed in a surface of the n-type semiconductor layer 32 and the surface is optically exposed.