INTRUSION DETECTION SYSTEM

The intrusion detection system includes a GNSS sensor that acquires a position of a work machine (20) at work in a work area (70), a LiDAR (2) that is disposed outside the work area (70) and acquires point cloud data indicating a distance up to an object located inside or outside the work area (70), a position calculation unit that calculates positions of respective points of the point cloud data, a specifying unit that specifies a portion corresponding to the work machine (20) from the point cloud data as specific data, based on the position of the work machine (20) and the positions of the respective points of the point cloud data, and a detection unit that detects that an object has entered the work area (70), based on the point cloud data excluding the specific data.