To solve a problem that a diameter of a wheel is enlarged or the technique of a crawler or the like is applied to travel over the difference in level such as steps, the off-road, and the like, and it is very difficult for practi cal small wheels to travel over the difference in level such as steps, off-road and the like, as theoretically, conventional wheels can not travel over the differ ence in level such as the steps over 1/2 of their diameter.

Plural wheels are arranged in series, and a common axle part of plural wheels can be freely rotated, or driven and rotated, so that the wheels can run over the difference in level or the like of approximately a little over 1/2 of a diameter of the wheel by the power of approximately 1/2 or less by applying the principle of the lever, when the wheels touches the difference in level or the like.