To correct distortion aberration satisfactorily and prevent shading, by providing a solid image pickup element for generating larger output to luminous flux entering a light receiving face in the state of inclining outward from the optical axis more than luminous flux vertically entering the light receiving face as being separated farther from the center part of the light receiving face.

A meniscus lens with a concave side facing the object side is used for a fourth group 6 arranged closest to the image side out of lens components constituting an objective lens system 1 so as to improve on such defectiveness that large distortion aberration is generated besides the whole length becomes long and lens bore becomes large, which are the defects of a retrofocus type endoscope objective lens system. In addition, a CCD 2 is used to generate higher output from a photoreceptor positioned farther from the center part (coinciding with the optical axis of the objective lens system 1) of a light receiving face, that is, the output of a photoreceptor having a tendency to receive oblique light is made higher than a photoreceptor receiving incident light close to the vertical. The generation of luminance shading in the CCD 2 is thereby prevented.