To side-move, that is, to easily transfer laterally in a direction which intersects against the travel direction by installing a passive traveling measure such as a passive wheel, by which it is possible to go in and out of a direction of traveling freely, and in addition, by which it is possible to move to a direction which intersects against the traveling vehicle.
At both supporting frames, wheels 22a, 22b and wheels 30a, 30b are mounted in free rotation, and further, each electric motor is installed as a source of travel driving force. There, in a passive traveling measure, a passive wheel 52 is protruded to the direction of surface of a wall, and a driving wheel 22a is made to be separate from the surface of the wall. And when driving-wheels 30a, 30b travel in the direction of arrow head A, the whole device rotates in right direction taking a contact part P between a driving-wheel 22b and the surface of the wall as the center of rotation (central point of the device moves to the C direction). At this time, the passive wheel 52 of the passive traveling measure is passively moved to the direction shown in arrow head B. In this way, the side-move is possible if the passive traveling measure is used.