or rearward in the associated shield tubes 44 46 and 48 thereby to pivotally move the mirror unit about the spherical projection 64a of the mirror holding portion 64 into a desired angular position the setting of the wire assemblies is made in the following manner first one end of each wire 24 26 or 28 is passed leftward as viewed in fig2 through the opening 64b of the mirror holder portion 64 and then through an opening 22b formed in the back frame 22 of the mirror unit with the enlarged stopper head 24a 26a or 28a inclined upon the stopper head projecting sufficiently into the interior of the mirror unit the wire is pulled rightward causing the associated stopper head to be raised up and brought into engagement with the inside surface of the back frame 22 of the mirror unit then one end of the associated shield tube 44 46 or 48 is fixed or screwed to the opening 64b of the mirror holder portion 64 then the other end of the wire 24 26 or 28 is passed through the opening of the body 36 of the control device 30 and connected to the universally pivoting member 34 of the same and the other end of.