in detail with reference to the drawings fig1 and 3 show an interchangeable zoom lens barrel adapted for a single lens reflex camera as a first embodiment of the invention fig1 is a perspective view showing a flare cut stop portion in the first embodiment fig2 and 3 are sectional views showing in part the zoom lens barrel fig2 shows the zoom lens barrel in a telephoto end position of zooming while fig3 shows the zoom lens barrel in a wide angle end position of zooming referring to fig2 the lens barrel is provided with a mount 1 for mounting the lens barrel on a camera body a fixed tube 2 is arranged to have the mount 1 secured thereto and to support a guide tube 3 which is an internal structural member of the lens barrel the guide tube 3 has a cam tube 4 fitted on the outer diameter side thereof and lens units fitted in the inner diameter side thereof the cam tube 4 has a bayonet groove 4a formed in its inner circumferential side a bayonet claw 3a which is formed on the guide tube 3 engages the bayonet groove 4a by virtue of this arrangement the cam tube 4 is supported by the guide tube 3 so as to be rotatable around an optical axis a zoom ring 5 has a zoom operation part 5a which appears on the outside of the lens barrel and has a fixing part 5b where the zoom ring 5 is secured to the cam tube 4 by means of a screw or the like the zoom ring 5 is thus arranged to be rotatably supported by the guide tube 3 in such a way as to be rotatable around the optical axis together.