The lens barrel includes a first frame, a second frame, a drive actuator, and a transmission mechanism that transmits the drive force of the drive actuator. The second frame includes a substantially cylindrical main body, a gear portion, and cam grooves that include an inflection point in the range in which the zoom ratio of the optical system is varied. The transmission mechanism includes a first transmission gear portion that engages with a gear, a second transmission gear portion that is provided coaxially with the first transmission gear portion, and a clutch between the first transmission gear portion and the second transmission gear portion. The clutch temporarily disengages the drive force of the drive actuator transmitted to the first transmission gear portion, only with respect to rotation in one direction.