A planing machine includes a support bed disposed within a machine body. A rod unit is mounted on the machine body, and is operably associated with the bed such that rotation of the rod unit results in movement of the bed within the machine body. A slide element is disposed slidably on the rod unit, and carries first and second bevel gears thereon. A toothed driving wheel is disposed adjacent to the slide element. The bevel gears are coupled to the rod unit for co-rotation therewith. The slide element is movable on the rod unit to a first position, where the first bevel gear meshes with and is driven by the driving wheel to permit the rod unit to rotate in a first direction, and to a second position, where the second bevel gear meshes with and is driven by the driving wheel to permit the rod unit to rotate in a second direction that is opposite to the first direction.