To provide a diaphragm opening and closing mechanism for a zoom lens barrel, which can prevent the increase of size of a member having grooves formed for moving a frame of a group of moving lenses in the direction of optical axis.

The diaphragm opening and closing mechanism for the zoom lens barrel includes: the cam groove 63 formed in a restricting lever 62; and a cam pin 72 fitted into the cam groove formed in an idle running lever 71 in a width direction without causing a clearance and sliding in the cam groove in accordance with changes of a position in the direction of optical axis of the frame of the group of moving lenses to change a rotating position of the idle running lever, which in turn is provided with a function as a time difference power transmission mechanism.