To easily adjust the height position of a worktable (and an instrument holder) by allowing a single worker to open/close the locking by a foot operation and adjust the height position of the worktable by a hand operation.

A foot operation lever 10 is provided for adjusting the height of the worktable 2 (and the instrument holder 3) in a dental treatment unit. The foot operation lever 10 is pressed down to move a suspension portion 71 provided in an arm 7 extending from the side of the worktable 2 relative to a vertical portion 61 of an arm 6 extending from the side of the base 5 and adjust the height position of the worktable 2. After the adjustment, when the press-down force of the lever 10 is released, the suspension portion 71 is locked to the vertical portion 61.