PROBLEM TO BE SOLVED: To highly accurately and automatically detect a profile of a tunnel on the basis of three-dimensional coordinate data of a cloud of points extracted from a feature surface.SOLUTION: Subspace setting means 20 divides a profile neighborhood space that is along a cut plane and has a preset width in the depth direction orthogonal to the cut plane, into a grid shape, and sets a plurality of subspaces. Edge search means 22 searches for, within the cut plane for each subspace, a belt-like area having a predetermined width that is an edge approximate area in which a cloud of points projected on the cut plane are accumulated equal to or more than a criteria preset in the area and the cloud of points in the area has distribution width equal to or more than a threshold preset in the depth direction. The edge search means searches for a directional line along a distribution in the cut plane of the cloud of points belonging to the edge approximate area on the cut plane as the edge as a position of th
