A front-illuminated type photodiode array (PDA1-PDA4) in which a plurality of photodetecting channels for detection target light to be entered thereinto are formed on a silicon substrate having a semiconductor layer of a first conductivity type, the photodiode array comprising: an epitaxial semiconductor layer of a second conductivity type formed on the semiconductor layer of the first conductivity type, forming pn junctions at an interface to the semiconductor layer, and having a plurality of multiplication regions for avalanche multiplication of carriers generated with incidence of the detection target light, so that the multiplication regions correspond to the respective photodetecting channels; a plurality of semiconductor regions of the second conductivity type formed in the epitaxial semiconductor layer; and a plurality of resistors each having two end portions, provided for the respective photodetecting channels, and each electrically connected through one of the end portions to the epitaxial semiconductor layer and connected through the other of the end portions to a signal conducting wire, wherein each multiplication region is a region near the interface to the silicon substrate in the epitaxial semiconductor layer located below the semiconductor region in the lamination direction of semiconductor layers, wherein an irregular asperity is formed in at least a surface corresponding to the photodetecting channels in the semiconductor layer of the first conductivity type, wherein at least the surface corresponding to the photodetecting channels in the semiconductor layer of the first conductivity type is optically exposed, and wherein a surface opposed to the surface with the irregular asperity formed therein constitutes a light incident surface and light incident from the light incident surface travels in the semiconductor layer. an epitaxial semiconductor layer of a second conductivity type formed on the semiconductor layer of the first conductivity type, forming pn junctions at an interface to the semiconductor layer, and having a plurality of multiplication regions for avalanche multiplication of carriers generated with incidence of the detection target light, so that the multiplication regions correspond to the respective photodetecting channels; a plurality of semiconductor regions of the second conductivity type formed in the epitaxial semiconductor layer; and a plurality of resistors each having two end portions, provided for the respective photodetecting channels, and each electrically connected through one of the end portions to the epitaxial semiconductor layer and connected through the other of the end portions to a signal conducting wire, wherein each multiplication region is a region near the interface to the silicon substrate in the epitaxial semiconductor layer located below the semiconductor region in the lamination direction of semiconductor layers, wherein an irregular asperity is formed in at least a surface corresponding to the photodetecting channels in the semiconductor layer of the first conductivity type, wherein at least the surface corresponding to the photodetecting channels in the semiconductor layer of the first conductivity type is optically exposed, and wherein a surface opposed to the surface with the irregular asperity formed therein constitutes a light incident surface and light incident from the light incident surface travels in the semiconductor layer.