To provide a mechanism for adjusting the height of a top board which is easy to adjust the height and repeatably return to the original height, and with which the height of a top board is readily determined.

The mechanism for adjusting the height of a top board has a link mechanism provided between a top board and a base, and changing the crossing angle of the link mechanism to vary the height of the top board, wherein a first link has a lower end turnably pivoted at the base and an upper end swingably supported at the top board, and a second link has an upper end turnably pivoted at the top board and a lower end swingably supported at the base. The mechanism includes: a locking rod horizontally extending substantially perpendicular to the swinging direction from the vicinity of the upper end of the first link; and a locking piece having a plurality of locking grooves engaging to the locking rod to restrict the swing of the locking rod, along the swinging direction of the locking rod, and making each of the locking grooves removably operate to the locking rod. The end of the locking rod projects outward from the top board or base.