later the pivotal motions of the aforementioned arm 14 are transmitted to the arm 16 by means of a link 17 the pivotal motions of the arm 16 are transmitted to the steering ski 10 through links 18 and 19 the connecting pins 20 21 and 22 between the adjacent two of the arm 16 the links 18 and 19 and the steering ski 10 are attached so that they are directed sidewise of the chassis when the steering ski 10 is in its forward direction the connecting pins are therefore parallel to one another a pipe 30 is fixed to frame 1 stationary cylinder 31 is inclined so that its lower end is positioned in front of its upper end a movable cylinder 32 is held in the stationary cylinder 31 such that it can move up and down and also rotate movable cylinder 32 protrudes upward and downward from the stationary cylinder 31 and steering ski 10 is mounted to its lower end for this purpose a bracket 33 is fastened and fixed to the lower end of movable cylinder 32 bracket 33 is inserted into the opening 35 of a mounting member 34 that has a c shaped section which is integrally fixed to the upper sides of steering ski 10 and is attached by means of a through bolt 37 which extends through the bracket 33 to cross the steering ski 10 as well as the side walls 36 of opening.