A lens barrel has a focusing operation and a zooming operation which are carried out with only one driving source which is installed outside the lens barrel so as to realize a most suitable resolution for each of the operations. A rotary cylinder which supports a zooming frame which is axially movably therein, is connected to a linear-moving cylinder with a bayonet, which is axially movably supported inside a fixed cylinder. A focus rotation transmission key of a driving cylinder drives a lens frame which engages the zooming frame by a connecting helicoid. A zooming rotation transmission key of the driving cylinder engages an edge surface, forming a rotation transmission groove, of the rotary cylinder, with a play range. Upon rotation of the driving cylinder, only the lens frame is rotated to operate a focusing operation within the play range; however, the rotary cylinder is rotated to operate a zooming operation when the key contacts the edge surface of the rotary cylinder.