A lens barrel includes a movable lens unit movable in an optical-axis direction, an actuator configured to move the movable lens unit in the optical-axis direction, a guide member configured to guide the movable lens unit in the optical-axis direction, and a guide-member-holding portion holding the guide member. The circuit board structure includes non-conductive material defining a top surface of the circuit board structure and a bottom surface of the circuit board structure, vias supported by the non-conductive material, top pads electrically coupled to the vias, and bottom pads electrically coupled to the vias. Other embodiments are described and claimed. The six torque-transmitting mechanisms provide interconnections between various gear members, and with the transmission housing, and are operated in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio. The address controller sequentially accesses memory cells selected by the start address and the incremented start address in response to a transition of the second clock signal.