A lens barrel is proposed, in which the optical adjustment of its lens system can be performed easily and at a reduced cost, and also an optical instrument having such a lens barrel is provided. A lens barrel is provided, which comprises: a lens frame for holding a lens; a holding frame for holding the lens frame; and an adjustment mechanism which, while allowing the lens frame to be pressed and fit into the holding frame thereof with a predetermined abutting force resulting from an elastic force, and while retaining its fit-in state, can adjust a position of the lens frame with regard to said holding frame in the directions of an optical axis via a plurality of stepwise stages by rotating said lens frame around its own axis of rotation.