A photodiode array (1, 30, 40, 50) in which a plurality of photodetector channels are formed on a substrate having a first semiconductor layer of a first conductivity type, with a light to be detected being incident to the plurality of photodetector channels, said photodiode array comprising: the substrate; a semiconductor layer of a second conductivity type which is formed on the first semiconductor layer of the first conductivity type of the substrate and forms a pn junction at the interface with the first semiconductor layer, and also has 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, the photodetector channels arranged in a matrix including two columns; characterized in that the semiconductor layer of the second conductivity type is an epitaxial semiconductor layer, and in that said photodiode array further comprises a second semiconductor layer of the second conductivity type, arranged at a light incident side of the epitaxial semiconductor layer, having a higher impurity concentration than that of the epitaxial semiconductor layer, and having a plurality of regions arranged corresponding to the multiplication regions; and a plurality of resistors each of which has two ends (4a, 4b) and is provided for each of the photodetector channels in the two columns so as to be electrically connected to the epitaxial semiconductor layer via one end thereof and be connected to a common signal conductor via the other end thereof, wherein, the photodetector channels in the two columns are arranged adjacent to the common signal conductor such that the common signal conductor is provided between the two columns of photodetector channels. the substrate; a semiconductor layer of a second conductivity type which is formed on the first semiconductor layer of the first conductivity type of the substrate and forms a pn junction at the interface with the first semiconductor layer, and also has 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, the photodetector channels arranged in a matrix including two columns; characterized in that the semiconductor layer of the second conductivity type is an epitaxial semiconductor layer, and in that said photodiode array further comprises a second semiconductor layer of the second conductivity type, arranged at a light incident side of the epitaxial semiconductor layer, having a higher impurity concentration than that of the epitaxial semiconductor layer, and having a plurality of regions arranged corresponding to the multiplication regions; and arranged at a light incident side of the epitaxial semiconductor layer, having a higher impurity concentration than that of the epitaxial semiconductor layer, and having a plurality of regions arranged corresponding to the multiplication regions; and a plurality of resistors each of which has two ends (4a, 4b) and is provided for each of the photodetector channels in the two columns so as to be electrically connected to the epitaxial semiconductor layer via one end thereof and be connected to a common signal conductor via the other end thereof, wherein, the photodetector channels in the two columns are arranged adjacent to the common signal conductor such that the common signal conductor is provided between the two columns of photodetector channels.