To assure the safe and stable operation of a discharge device and a radar device by installing a folding type ground increase plate for increasing a ground area on the ground plate connected to the lower end of a leg part and expanding the ground increase plate by an expansion device automatically.

An outrigger 1 has a beam part 2 arranged in front/rear and right/left sides of a vehicle and telescoped in a horizontal direction and a leg part 3 telescoped in a vertical direction and a ground plate 4 is installed on the lower end of the leg part 3. A ground increase plate 5 folded vertically by a hinge 6 for the four sides of the ground plate 4 is installed and a hydraulic expansion device 7 is jointed to the leg part 3 and the ground increase plate 5. The leg part 3 is lowered by a hydraulic device at the operation time and further the ground increase plate 5 folded vertically is fallen by the hydraulic expansion device 7 and expanded upto the horizontal state for the ground plate 4 and grounded. Thus, the grounding pressure is reduced by increasing the ground area by the worth of the area of the ground increase plate 5.