PURPOSE: To prevent reduction in sensitivity by grouping plural photodetector elements, and forming each group on a corresponding common electrode to decrease stray capacity to be produced between the common electrode and a light shield member.

CONSTITUTION: A reflected light of an original 22 passes through a transparent electrode 17 near a light transmitting layer 20 and is received by a photoconductor 16. On the other hand, the common electrodes P1, P2 are formed on an insulation layer 15 with a gap W, the light shield member 14 has a size required to prevent the light from a fluorescent light 21 from passing through the gap W and is overlapped slightly at the lower part of the common electrodes P1, P2. Thus, the stray capacity to be produced between the common electrodes P1, P2 and the light shield member 14 is suppressed to slight thereby preventing the deterioration of the reader in sensitivity. This is applied similarly also to other groups.