Provided are a free-form lens and free-form mirror having excellent molding properties, a method for designing the same, and a projection-type image display device using the same. An embodiment of the present invention is a free-form lens molded from a transparent resin for configuring an oblique-projection optical system including a free-form mirror in a projection-type image display device, the free-form lens being provided with a lens effective region in which a predetermined free-form face is formed on a surface thereof, and an edge face formed so as to surround the lens effective region, the lens effective region and the edge face in a portion of the periphery surrounding the lens effective region where the edge face is not formed being connected by a flat face and/or a curved face in the vicinity of the lens effective region, the flat face and/or curved face being set so that the direction of inclination of the lens effective region does not change, and an end face including the curved face and/or the flat face being configured as a tapered face.