PURPOSE: To make it possible to set an optimum course by dividing a gliding plate having two cutters into the plural number of gliding plates having different pitch spaces of the cutters, and providing one of the split gliding plates on the snow so that it is capable of selection.

CONSTITUTION: A plurality of gliding plates 4a, 4b... having different pitch spaces of two cutters 5 and 5 to form two gliding channels of a course are provided to a frame 3 mounted to a snowmobile 1 through a hydraulic cylinder 2 so that it is capable of vertical motion. After that, the plural number of gliding plates 4a and 4b are pivoted on a rotary bracket 7 through one end of a pin 8 and the other end of a cylinder 9, the rotary bracket 7 is pivoted on a lower bearing arm 11a of the end of a lift frame 11 through a pivot 10 and, at the same time, they are connected between the lower bearing arm 11a and upper bearing arm 11b of the end of the lift frame 11 through a cylinder 12. After that, the lift frame 11 is pivoted on a rear operation machine 13.