PURPOSE: To provide high travelling performance by forming a grounding part of a sled into a curved shape, in side view, hating curvature radius of predetermined times as large as a tire radius, in a device in which a sled is installed in the front wheel part and an attachment consisting of caterpillar in the rear wheel part.

CONSTITUTION: A sled is attached to a front tire 5 and wheel 6 of a motorcycle by a constraint means 4 and a rear part of the sled 1 is connected to a fork 3, which does not allow relative displacement with a front wheel shaft, via a connection member 2 with a hard built-in spring device. In side view, this sled 1 is formed its grounding part into a curved shape having curvature radius of two times or twenty times as large as the tire radius and in the cross section perpendicular to the travelling direction, both end parts are formed into a downward curved shape. As for the rear wheel part, an attachment including a wound caterpillar 7 is attached between a drive pulley having same radius as the rear wheel and a guide pulley and the guide pulley 9 is pivotally mounted on a free end of a holding member 27 which is supported by a body frame 11 via the constraint means 12.