An elongated image sensor comprises a plurality of light receiving elements of a sandwich structure arranged in a row and wherein a photoconductive layer is sandwiched by a lower electrode and a light-permeable upper electrode. In the image sensor, an overlapped region of the lower and upper electrodes for each of the light receiving elements is made larger in area than a light reception region and the light reception area (sensor area) is defined by a light shielding means or an insulating film having an opening of a predetermined size.