A photodiode array includes a substrate of a common read-out control circuit; and a plurality of photodiodes arrayed on the substrate and each including an absorption layer, and a pair of a first conductive-side electrode and a second conductive-side electrode. In this photodiode array, each of the photodiodes is isolated from adjacent photodiodes, the first conductive-side electrodes are provided on first conductivity-type regions and electrically connected in common across all the photodiodes, and the second conductive-side electrodes are provided on second conductivity-type regions and individually electrically connected to read-out electrodes of the read-out control circuit.