A lens barrel assembly has a first groove formed in a stationary barrel. A second groove is formed in a rotatable barrel. A diaphragm control plate portion is disposed between an inner surface of the rotatable barrel and an iris diaphragm device in a rotatable manner in a circumferential direction, has an end portion connected to a driving ring. An engaging groove is formed in the diaphragm control plate portion to extend along the optical axis. An operable aperture ring is disposed outside the stationary barrel. A pin device has first and second end portions, the first end portion being secured fixedly to the aperture ring, the second end portion being inserted through the first and second grooves and the engaging groove, for operating upon rotation of the aperture ring to cause the engaging groove to rotate the diaphragm control plate portion to actuate the driving ring.