It is provided that a lens positioning jig, a method of attaching lens barrel, and a lens device. A lens holding portion is inserted through a barrel insertion hole, and then a housing holding portion allows a barrel attachment portion to be thereby positioned and held in a lens housing. When an air pump is operated, a lens holding portion sucks and holds a convergent lens held in a second lens barrel and then positioned with respect to the barrel attachment portion. In addition, the second lens barrel is held in the lens housing so that the second flange does not come in contact with barrel attachment groove. Subsequently, an adhesive is filled into a gap formed between the second flange and the barrel attachment groove to thereby fix the second lens barrel thereto.