A lens assembly has: optical members including lenses and spacing rings; and a ceramic lens frame into which the optical members are inserted. A solid lubricant is applied to at least one of a part of the inner peripheral surface of the ceramic lens frame, which part is to be in contact with at least the outer peripheral surfaces of the optical members, and the outer peripheral surfaces of the optical members. Subsequently, the lenses and spacing rings are alternately inserted into the ceramic lens frame and then pressed by a pressing ring.