According to the invention, an inward collar is integrally shaped on the inner periphery of a cylindrical boss portion. A substrate is provided having one or more pairs of sensors mounted thereon. A total area of the through holes in an upper half portion of the front side plate adjacent to the top plate is different from a total area of the through holes in a lower half portion of the front side plate adjacent to the bottom plate. The fifth lens element has a convex image-side surface. There are locking means for fixing the plant cord with respect to the suspension hook and thus supporting securing to the soundings.