It is to provide a wide-angle optical system for a solid image pickup device that favorably corrects distortion. The imaging lens is a biconvex lens, the object side face is formed into an aspheric shape in which the negative refracting power becomes stronger the farther the imaging lens is from an optical axis in the radial direction, and a condition expressed by the following expression (1) is to be satisfied; 0.8>|r.sub.1/r.sub.2|.gtoreq.0.5 (1) where, r.sub.1: center radius curvature of the object side face of the imaging lens r.sub.2: center radius curvature of the image surface side face of the imaging lens.