To improve maneuverability in cultivating work by arranging side balance weights in lateral directional both side places of a tractor under a gravity center position of the tractor.

When a tractor inclines in the width direction, a horizontal support lever 10 of a balance control device B also inclines in the shaft direction. At this time, the moments M1 and M2 trying to rotate in the mutually opposite direction by both balance weights 12 through both downward arm- shaped levers 11 are applied to the horizontal support lever 10. Here, when weight of both balance weights 12 is denoted by W, (M1=W×L1) is realized on the left side of the horizontal support lever 10, and (M2=W×L2) is realized on the right side. As a result, the moment being (M2-M1) acts with the horizontal support lever 10 as clockwise directional torque. Therefore, the leftward inclined horizontal support lever 10 rotates in the clockwise direction with the vicinity of the center G1 of gravity when the balance control device B is arranged as the almost center, and is restored in a horizontal shape.