The compaction vehicle having a speed adjustment member, a displacement detector, and a drive source controller further includes a calculation device between the displacement detector and the drive source controller, receiving the displacement S, and outputting a signal I calculated to the controller; a running speed setting switch for the operator operating ON at a desired running speed; a control signal memory device provided inside the calculation device and memorizing a signal I1 to the controller. In a normal operation, the calculation device outputs the signal I to the controller so that a running speed increases or decreases according to the displacement S, and when the switch is operated to ON, the calculation device maintains the ON state, and the displacement S is not less than a predetermined value, the calculation device outputs the signal I1 memorized in the memory device so as that the vehicle will run at a constant speed.