To rise while climbing an ascending staircase, decrease vertical movement of a car body and improve its stability, by selecting drive force transmission ratio of a drive force transmitting means so as to roll on a vertical surface of the staircase by a wheel leading to its end edge.

Two wheels 6a, 6b and 7a, 7b mounted in arm members 4L (R), 5L (R) and a main shaft are connected by a drive force tranmitting means, since the arm members 4L (R), 5L (R) are rotatably supported, by selecting drive power transmission ratio by a speed change means, the wheels 6a, 6b and 7a, 7b, by a mode competitively ascending a vertical surface of a staircase, can climbe the staircase. Accordingly, even a staircase having a step difference larger than a diameter of the wheels 6a, 6b and 7a, 75 can be easily climbed, the staircase can be stably climbed by decreasing vertical movement of a car body. A coefficient of friction in a staircase surface is small, even in a condition easily slipped, climbing can be surely made by a rotational mode.