Abstract: A semi-finished lens of plastic material which will be ground on the basis of a spectacles prescription to be completed as a myopia correcting single-focus lens is molded such that the convex surface is a spherical nonprocessed surface and the concave surface is a nonspherical molded surface which requires no grinding. Thus, a completed lens can be easily obtained by simply grinding the spherical convex surface. Further, the concave surface which is a nonspherical molded surface is formed as an ellipsoidal surface of revolution, hyperboloidal surface of revolution or other nonspherical surface which has a curvature providing spherical power or a combination of spherical power and astimgatic power and whose curvature decreases from the optical center toward the periphery, whereby the difficulty of grinding can be decreased and the completed lens is free from the warping of images due to spherical aberration and has an edge which is thin and makes a better appearance.