To easily, surely and freely attachably and detachably attach a base leg in front and back directions to the lower end part of a column while visually confirming a connection part.

Many vertically arranged vertically long locking holes 2 are perforated on the front surface of the column 1, a locking hook 10 provided with an upward locking piece 10a and a downward locking piece 10b is provided successively to the rear surface of a connector 9 in a vertical direction provided with a downward insertion part 9a on an upper end and the locking hook 10 is freely detachably locked to the locking hole 2 of the column 1. The downward tongue piece of a long dimension is provided successively to the rear surface of the base leg 11 in the front and back directions, the tongue piece is freely detachably fitted from an upper part to the insertion part 9a of the connector 9 and an adjuster 8 for height adjustment is provided on the lower surface of the base leg 11 and the column 1.