PURPOSE: To run a truck with a simple mechanism by providing a wheel unit having a wheel and the brake on one end of a reciprocating rod and a frame mounting the wheel units placed back to back in the opposite direction.

CONSTITUTION: A rod 1 has one end mounting a piston and the other end mounting a wheel 3. The wheel 3 is provided with a brake 4. The piston and a part of the rod 1 reciprocate in a cylinder 2 to provide a pneumatic cylinder. The pneumatic cylinders are mounted back to back to a frame 5. When first the rear wheel brake 4 is applied to pressurize air from 2 and 4, and front end advances. However, since the frame 5 is restricted by the rear wheel, it does not move. Next, when air is pressurized from 1 and 3, both wheels do not move and the frame 5 advances by L1. When only the brake 4 for the rear wheel 3 is released and air is pressurized to 1, 4, the rear wheel 3 advances by L2 and the front wheel 3 and the frame 5 do not move. A truck is advanced by the repetition of these operations.