sliding of the glass plate as shown in fig4 drive hook 33d of one supporter is connected to the lower part of one end 43a of drive wire 43 while the drive hook 33d of the other supporter is connected to the other end 43b of drive wire 43 as shown the intermediate portion of wire 43 is wound around pulleys 44 and 45 in a figure eight configuration pulley 45 is designed to rotate forward and backward by the action of a drive system comprising motor 25 and reciprocal clutch 63 the rotation of pulley 45 forward and backward moves the wire in a reciprocating manner as a result glass plate 31 and supporters 33 are reciprocated in the direction of arrow x springs 43c are disposed between each end 43a 43b of the wire and hook 33d to absorb shocks if it is desired not to utilize cover 37 as shown in fig8 the upper guide member 35 may be fixed by inserting plate 31 by a fastener 34 positioned through the hole 32 of glass plate 31 without the need of supporters 33 in this embodiment fastener 34 performs a function similar to that performed by supporter 33 this construction permits even a further reduction in the weight of the original carrier with an accompanying reduction in the necessary driving force on the upper surface of glass plate 31 a plastic scale plate 42 is positioned as shown in fig7 scale plate 42 contains an opening 42a having scale.