To improve the accuracy of an image by forking each of pixel having a square light receiving opening symmetric in the vertical and horizontal directions and having equal vertical and horizontal width to reduce the distortion due to the resolution difference depending in the direction.

The light receiving opening 12 has equal widths Wv and Hv in the vertical and horizontal directions V and H and made symmetric in these directions, this makes equal the quantities of a regular light L and oblique light L' and limits of incident lights in the directions V and H and hence equal the resolutions in both directions. This it is possible to form the receiving opening 12 in such square shape to make equal the resolutions in the directions H and V, resulting in reduction of the distortion of an input image.