PURPOSE: To perform stable ground support of a conveying vehicle by means of a number of earth wheels as the earth wheel is prevented from levitation and besides to reduce the change of the earth attitude of a conveying car body due to a conveyance weight.

CONSTITUTION: At least one spot A1 of three earth support positions A1, A2, and A3 in which earth support of a conveying car body 1 is effected is caused to effect earth support by a wheel support body 3 to support earth wheels 2a, 2b, and 2c in three support positions B1, B2, and B3, equivalent to the apex positions of a virtual triangle Q in a plane view. The wheel support body 3 is oscillatorily mounted on the conveying car body 1 side in such a state to allow relative rotation around virtual line segments D1, D2, and D3, which intercouple the remaining two support positions of three support positions B1, B2, and B3, in such a state that earth support of two spots A2 and A3, except the earth support position A1, is effected by the wheel support body 3. The operation center position of a load exerted on the wheel support body 3 by the conveying car body 1 side is arranged inside a virtual triangle Q.