A lens system suitable to be used with an imaging element having a quadrilateral shape with shorter sides and longer sides and disposed on an optical axis of the lens system, and comprising, in order from an object side to an image surface side, a first plurality of lens elements (L1, L2, L3, L4, L5), an aperture diaphragm, and a second plurality of lens elements (L6, L7, L8), all configured to form an approximately quadrilateral image on an image surface of the imaging element, wherein the first plurality of lens elements comprises at least a first free-curved lens that is asymmetrical with respect to the optical axis, and a free-curved surface of the first free-curved lens has negative refractive power with respect to a ray parallel to the optical axis at an intersection point between a circle separated from the optical axis by a length having a predetermined ratio, ranging from 40% to 80% inclusive, with respect to a minimum image height and a first surface passing through the optical axis and parallel to the longer sides of the imaging element, and positive refractive power with respect to a ray parallel to the optical axis at an intersection point between a circle separated from the optical axis by a length having the predetermined ratio with respect to the minimum image height and a second surface passing through the optical axis and parallel to the shorter sides of the imaging element, and a portion where positive and negative inversion occurs in refractive power of the free-curved surface, wherein the minimum image height is in the shorter side direction of imaging element and corresponds to a shortest one among distances on an image surface, from an image point by a ray entering perpendicularly onto said imaging element to an end of an image circle formed by the lens system, the second plurality of lens elements comprises at least a second free-curved lens that is disposed closest to the image surface side and has two surfaces that are free-curved surfaces facing the object side and the image surface side respectively. in order from an object side to an image surface side, a first plurality of lens elements (L1, L2, L3, L4, L5), an aperture diaphragm, and a second plurality of lens elements (L6, L7, L8), all configured to form an approximately quadrilateral image on an image surface of the imaging element, wherein the first plurality of lens elements comprises at least a first free-curved lens that is asymmetrical with respect to the optical axis, and a free-curved surface of the first free-curved lens has negative refractive power with respect to a ray parallel to the optical axis at an intersection point between a circle separated from the optical axis by a length having a predetermined ratio, ranging from 40% to 80% inclusive, with respect to a minimum image height and a first surface passing through the optical axis and parallel to the longer sides of the imaging element, and positive refractive power with respect to a ray parallel to the optical axis at an intersection point between a circle separated from the optical axis by a length having the predetermined ratio with respect to the minimum image height and a second surface passing through the optical axis and parallel to the shorter sides of the imaging element, and a portion where positive and negative inversion occurs in refractive power of the free-curved surface, wherein the minimum image height is in the shorter side direction of imaging element and corresponds to a shortest one among distances on an image surface, from an image point by a ray entering perpendicularly onto said imaging element to an end of an image circle formed by the lens system, the second plurality of lens elements comprises at least a second free-curved lens that is disposed closest to the image surface side and has two surfaces that are free-curved surfaces facing the object side and the image surface side respectively.