A method for manufacturing an optical element, such as a plastic lens or similar, by molding. The manufacturing method includes the steps of molding the plastic lens under a prescribed molding temperature higher than a glass transition level of the plastic material used to from the optical element. The manufacturing method also includes the step of gradually cooling the optical element by at least 5° C. with a speed which decreases by approximately 3° C. per minute. The optical element formed from a plastic material includes a substantially rectangular shape having a width, a height, and a thickness, wherein the width is greater than the height and the thickness is measured in an optical axis direction. The optical element also includes a refractive index distribution of approximately 2×10−5 at a central half section of the height. The optical element may be defined by the manufacturing method having the molding step and the gradual cooling step. The apparatus used to manufacture the optical element includes a molding device for molding the optical element under a prescribed molding temperature higher than a glass transition level of the plastic material forming the optical element and a device for gradually cooling the optical element.