Abstract: A vibratory compaction working machine has a lower travel structure and an upper swing structure mounted on the lower travel structure. The upper swing structure has a boom mounted thereon for pivotal movement by a first hydraulic cylinder, an arm mounted on the boom at its forward end for pivotal movement by a second hydraulic cylinder, and vibratory plate compactor mounted on the arm at its forward end for pivotal movement by a third hydraulic cylinder. The arm is in the form of an extension arm having a first arm element and a second arm element mounted for linear movement relative to the first arm element by a fourth hydraulic cylinder. The first arm element is attached at the forward end of the boom for pivotal movement by the second hydraulic cylinder, and the second arm element has the vibratory plate compactor attached to the forward end thereof for pivotal movement by the third hydraulic cylinder.