PURPOSE: To improve the efficiency of use of light and to realize a small-sized device, by the color resolution through the use of a transmission type diffraction grating.

CONSTITUTION: An image of an objective is formed near a diffraction grating K with an optical system L having an aperture F, and the image is projected on a picture element plane of a solid-state image pickup element T via a distributed refractive factor type fiber plate S located at the back of the grating K. In each fiber of the fiber plate S, the lengthwise direction has a prescribed angle to the optical axis of the image pickup optical system. The element T receives the 1st order diffractive image. That is, at the end of the fiber plate S, red, green and blue component light are incident and resoluted for color to produce signals on picture element of each color component on the element T.