A clustering method of point cloud data, the method comprising: a point cloud data acquisition step of acquiring, by a laser scanner, point cloud data from a region including a measurement target object, from above the measurement target obj ect; and by a data processing section that performs arithmetic processing on the point cloud data, a plane clustering step of clustering, as a planar cluster, the point cloud data corresponding to a top surface of the measurement target obj ect, among the acquired point cloud data; a reference planar cluster extraction (STEP-501) step of extracting a reference planar cluster (CL1A) that is the planar cluster to be a same-region determination reference; a planar cluster search step (STEP-503) of calculating a difference between elevation values (ΔH) of the reference planar cluster (CL1A) and the planar cluster other than the reference planar cluster (CL1A), and of searching for the planar cluster for which the difference between the elevation values (ΔH) is equal to or smaller than a predetermined threshold; a planar cluster selection step (STEP-504) of selecting one planar cluster for which the difference between the elevation values (ΔH) is equal to or smaller than the predetermined threshold; an overlap detection step (STEP-505) of detecting overlap/non-overlap of the reference planar cluster (CL1A) and the one planar cluster; and a same-region clustering step (STEP-506) of clustering, as a same-region cluster, the reference planar cluster (CL1A) and the one planar cluster, in a case where an overlap is detected, a planar cluster presence/absence determination step of determining presence/absence of another planar cluster other than the one planar cluster found in the planar cluster search step (STEP-503), wherein the planar cluster selection step (STEP-504), the overlap detection step (STEP-403, STEP 505), and the same-region clustering step (STEP-506) are repeated in an order mentioned by the data processing section after the planar cluster presence/absence determination step, until absence of the other planar cluster is determined in the planar cluster presence/absence determination step. a point cloud data acquisition step of acquiring, by a laser scanner, point cloud data from a region including a measurement target object, from above the measurement target obj ect; and by a data processing section that performs arithmetic processing on the point cloud data, a plane clustering step of clustering, as a planar cluster, the point cloud data corresponding to a top surface of the measurement target obj ect, among the acquired point cloud data; a reference planar cluster extraction (STEP-501) step of extracting a reference planar cluster (CL1A) that is the planar cluster to be a same-region determination reference; a planar cluster search step (STEP-503) of calculating a difference between elevation values (ΔH) of the reference planar cluster (CL1A) and the planar cluster other than the reference planar cluster (CL1A), and of searching for the planar cluster for which the difference between the elevation values (ΔH) is equal to or smaller than a predetermined threshold; a planar cluster selection step (STEP-504) of selecting one planar cluster for which the difference between the elevation values (ΔH) is equal to or smaller than the predetermined threshold; an overlap detection step (STEP-505) of detecting overlap/non-overlap of the reference planar cluster (CL1A) and the one planar cluster; and a same-region clustering step (STEP-506) of clustering, as a same-region cluster, the reference planar cluster (CL1A) and the one planar cluster, in a case where an overlap is detected, a planar cluster presence/absence determination step of determining presence/absence of another planar cluster other than the one planar cluster found in the planar cluster search step (STEP-503), wherein the planar cluster selection step (STEP-504), the overlap detection step (STEP-403, STEP 505), and the same-region clustering step (STEP-506) are repeated in an order mentioned by the data processing section after the planar cluster presence/absence determination step, until absence of the other planar cluster is determined in the planar cluster presence/absence determination step.