A foreign body detection system includes a first point cloud acquisition unit and a second point cloud acquisition unit as a point cloud acquisition means, an alignment unit, and a foreign body detection unit. The point cloud acquisition means acquires a point cloud by controlling a first fixed-point three-dimensional LiDAR scanner in such a way that the first fixed-point three-dimensional LiDAR scanner performs scanning in a scanning range including a monitoring target in a scanning range and generates a point cloud. The alignment unit aligns the point cloud and known three-dimensional shape data about the monitoring target with each other. The foreign body detection unit detects a foreign body in contact with the monitoring target, based on the point cloud and the aligned three-dimensional shape data.