An interchangeable lens unit comprises a lens housing, a cam frame, and a zoom drive unit. The zoom drive unit is mounted to the lens housing, and rotationally drives the cam frame with respect to the lens housing. The lens housing has a substantially cylindrical main body component and a gear component that is disposed on the inner peripheral face of the main body component and to which the drive force of the zoom drive unit is transmitted. The gear component is disposed substantially in the middle of the main body component in the optical axis direction.