To get over a different level without any assistance by applying a constitution that drive power from a drive power generation mechanism is applied to one of front or rear wheel constitutional bodies, and further transmitted to the other front or rear wheel conditional bodies.

Rear wheel constitutional bodies 3 are driven with a drive power generation device 21 using a battery as an energy source, for example, on the operation of a motor. In addition, gears 6 and 6 different from each other in diameter and number of teeth are integrated with the axles 5 and 5 of the front and rear constitutional bodies 2 and 3, and a drive power transmission body 7 such as a chain is extended between the gears 6 and 6. As a result, the rear wheel constitutional bodies 3 are driven on the operation of the drive power generation device 21, and the front wheel constitutional bodes 2 are as well driven via the drive power transmission body 7. In this case, drive power can be transmitted to the front wheel constitutional bodies 2 via a constant velocity joint laid between the gear 6 and the axle 5. According to this construction, a different level can be got over using the drive power without any assistance, as far as the different level is approximately a half of a front wheel.