A lens barrel drive mechanism includes a system for detecting the number of revolutions of the output shaft of a motor, which is associated with the amount of extension of the lens barrel to which the rotating force of a gear in a gear train is transmitted. The second image display panel has a structure in which light incident from a back surface side of the second image display panel is transmitted toward a side of an image display surface of the second image display panel, and overlaps with an image display surface of the first image display panel. The baffle also reduces the critical volume of the welding machine and allows the fan to operate more efficiently and pull an increased amount of cooler ambient air through the machine which creates a greater cooling effect during the cooling cycle of the machine. Similar stents may be used in other body areas, such as in draining the biliary tract, the gastro-intestinal tract, hepatic procedures, and in vascular procedures as well.