The inventive lens barrel comprises: a first group frame 12 retaining the first group lens 21 with a positive refractivity and being movable on the optical axis; a second group frame 11 retaining the second group lens 22 with a negative refractivity and being movable on the optical axis; a third group frame 10 retaining an aperture diaphragm 10b and the third group lens 23, and being movable on the optical axis and pivotable perpendicular to the optical axis in such a manner that the third group frame 10 can move the aperture diaphragm 10b and the third group lens 23 to the position on the optical axis O in a imaging standby state, in which the lens barrel 1 is extended, and move them to the position out of the optical axis O in the retracted state, in which the lens barrel 1 is shortened; and, a fourth group frame 13 retaining the fourth group frame 24 with a positive refractivity, and being movable on the optical axis, and being arranged such that it can retract the aperture diaphragm 10b and the third group lens 23 to a space between the object side end of the second group image side lens of the second group lens 22, which has a relatively smaller outer shape, and the image side end of the fourth group lens 24, in view from the direction perpendicular to the optical axis, under the retracted state.