An optical system includes a plurality of lenses. The plurality of lenses have refractive index distributions in which a refractive index changes in directions orthogonal to optical axes. The optical axes of the plurality of lenses are disposed on the same straight line as each other. The plurality of lenses are manufactured on the basis of same design values relating to an on-axis refractive index and a refractive index distribution constant. When rotation positions around the optical axes of the plurality of lenses at which a total aberration amount of the plurality of lenses reaches a maximum are set as reference rotation positions for the plurality of lenses, any one of the plurality of lenses is arranged at a position acquired by relatively rotating the reference rotation position around the optical axis.