To enable the effective utilization of a space below a lift body while making an operation handle rotate stably.

A turning rod 17 directed longitudinally at a crank-like operation handle 15 is slidably fitted axially while being unrotatable relatively onto the front end part of a drive rod 13 which is disposed so as to be directed longitudinally below a liftable top board 7 while being linked to a lift mechanism for lifting or lowering the top board 7. The operation handle 15 is made movable between an operable position on the front of the top board 7 and a housing position of being housed below the top board 7.