PURPOSE: To ensure stabilized running by deciding one wheel out of a couple of wheels on one side rail as a driving wheel and one wheel on the other side rail as a driven wheel, in a rail running truck running on two rails by three wheels.

CONSTITUTION: In a running truck 10 running on rails R, a driving wheel 2 and a driven wheel 3 are installed on the front & rear of the one side of its chassis 10 to make one side rail R move by rolling. The driving wheel 2 and the driven wheel 3 are respectively fixed rotatably in an arrow mark direction C with a supporting shaft 11 as their center. Also, a driven wheel 12 is installed almost in the central position on the opposite side of the chassis 10 to make the other side rail move by rolling. This driven wheel 12 is attached to the chassis 10 through a crank type rotatable shaft 13, and it is installed in the state capable of proceeding and receeding in an arrow mark direction D as well rotatating in the arrow mark direction C through the shaft 13.