PROBLEM TO BE SOLVED: To precisely detect a compaction position of a compaction operation by a work machine by utilizing a GPS.SOLUTION: A compaction attachment 7 is mounted atop of a movable arm member 3 of a work machine 1 having the arm member having one end supported on a moving swivel base 2, GPS antennas 12a, 12b are fitted to the swivel base 2 of the work machine 1, and the arm member 3 or compaction attachment 7, respectively, and an inclinometer 16 is fitted to the arm member 3. While the work machine 1 is moved within a compaction area E, three-dimensional coordinates of a grounding point P of the compaction attachment 7 are calculated from observation signals of the GPS antennas 12a, 12b and an observation signal of the inclinometer 16, and a compaction state on the compaction area E is managed according to the three-dimensional coordinates of the grounding point P of the compaction attachment 7. Preferably, a concrete vibrator 10 is used as the attachment 7, and the concrete compaction state is ma
