A high-NA and thin objective lens which prevents occurrence of a crack during lens molding and can stably be molded is provided. The present invention is directed to an objective lens having an optical surface having power which is not negative. The objective lens is a single lens and is formed such that a flat portion which is provided at an outer peripheral portion and perpendicular to the optical axis is closer to a disc surface than the position of the top of an exit-side surface of the objective lens and such that the rate of change in sag of the exit-side surface is continuous across the entire region.