PROBLEM TO BE SOLVED: To enable continuous running at a high speed.
SOLUTION: This wheel set having a gauge variable mechanism has a structure where a running torque of a main electric motor is transmitted via a roll spline 1 disposed between an axle 2 and a wheel 3 to the wheel 3 that is mounted to the axle 2 via a slide bearing 7 and is moved with respect to the gauge in the axial direction of the axle 2 and fixed in position to integrally rotate the axle 2 and the wheel 3. A bearing device 21 is disposed at the center position of the axle 2 and the roller spline 1 is disposed between the wheel 3 and the bearing device 21, thereby miniaturizing axle bearings 8 disposed at both ends of the axle 2 and reducing the unsprung mass. A position fixing device 11 of the wheel 3 is disposed in a shaft end of the axle 2 having the axle bearings 8. The axle bearings having a size equal to that of a normal wheel set can be used, so that temperature increase of the bearings or sealing property of lubrication that are caused by increase of circumferential speed can be solved and continuous running at the high speed is possible.