PURPOSE: To prevent a main tube in a conventional unit for dentistry from sagging and from being hooked when an instrument is stored.

CONSTITUTION: A bracket 5 for fixing is mounted on the rear side of a table 4 and a spring case 6a is fixed on the rear side of the bracket 5 and a double- wound clockwork spring apparatus 6 is built in the spring case 6a. A wire roller 8a is freely rotatably projectedly provided on its rear end to energize a clockwork spring 7 in the winding direction (the direction A) and the wire 8 is energizeed in the same direction as that for the spring 7 through a spring roller 7a which plays a role also as a spring and a hanging ring-type pulley 9 on the apex of the wire 8 is pulled up backward through the wire roller 8a and an inserted main tube is always pulled to prevent it from sagging.