PURPOSE: To eliminate metal percussing noise at the time of running on the bad road in such a way that elastic ring is inserted between a cylinder bore and rack guide, the rack guide is buffered and supported.

CONSTITUTION: A rack guide element 10 is housed in free command of sliding in a cylinder bore 9 by inserting an O ring 16 on its annular groove 15. When running on the bad road, even if radial directional impact force is applied to the rack guide element 10 and the cylinder bore 9, both cannot contact directly each other by buffering action of the O ring 16. and likewise, since impact force in the direction to draw the rack guide element 10 near to a cover element 13 is absorbed by elasticity of the O ring 16 as well as friction between the O ring 16 and the cylinder bore 9, it eliminates the possibility of contacting the rack guide element 10 and the cover element 13 with impact. Thus, metal percussing noise can be eliminated when running on the bad road.