A top surface estimation method for a measurement target object, the method comprising: by a data processing section that performs arithmetic processing on point cloud data, a two-point selection step of extracting the point cloud data included within a predetermined thickness of a region in a vertical direction, from the point cloud data, acquired by a laser scanner from above a measurement target object, of the region including the measurement target object, and selecting two points from the point cloud data extracted; an inter-point distance calculation step of calculating an inter-point distance between the two points; a two-points-on-plane deeming step of deeming the two points to be two points that are on a same plane, in a case where the inter-point distance calculated is equal to or smaller than a predetermined threshold; characterised by: a center-of-gravity calculation step of calculating a center of gravity of points that are deemed to be on the same plane; a neighboring point search step of searching for a neighboring point that is a point, a distance of which to the center of gravity is equal to or smaller than the threshold; and a neighboring-point-on-plane deeming step of deeming, in a case where the neighboring point is found, that the neighboring point is a point that is on the same plane as the points that are deemed to be on the same plane, wherein the center-of-gravity calculation step, the neighboring point search step, and the neighboring-point-on-plane deeming step are repeated in an order mentioned every time the neighboring point is detected, a plurality of points that are deemed to be on the same plane are acquired, and a top surface of the measurement target object is estimated based on the plurality of points. by a data processing section that performs arithmetic processing on point cloud data, a two-point selection step of extracting the point cloud data included within a predetermined thickness of a region in a vertical direction, from the point cloud data, acquired by a laser scanner from above a measurement target object, of the region including the measurement target object, and selecting two points from the point cloud data extracted; an inter-point distance calculation step of calculating an inter-point distance between the two points; a two-points-on-plane deeming step of deeming the two points to be two points that are on a same plane, in a case where the inter-point distance calculated is equal to or smaller than a predetermined threshold; characterised by: a center-of-gravity calculation step of calculating a center of gravity of points that are deemed to be on the same plane; a neighboring point search step of searching for a neighboring point that is a point, a distance of which to the center of gravity is equal to or smaller than the threshold; and a neighboring-point-on-plane deeming step of deeming, in a case where the neighboring point is found, that the neighboring point is a point that is on the same plane as the points that are deemed to be on the same plane, wherein the center-of-gravity calculation step, the neighboring point search step, and the neighboring-point-on-plane deeming step are repeated in an order mentioned every time the neighboring point is detected, a plurality of points that are deemed to be on the same plane are acquired, and a top surface of the measurement target object is estimated based on the plurality of points. a center-of-gravity calculation step of calculating a center of gravity of points that are deemed to be on the same plane; a neighboring point search step of searching for a neighboring point that is a point, a distance of which to the center of gravity is equal to or smaller than the threshold; and a neighboring-point-on-plane deeming step of deeming, in a case where the neighboring point is found, that the neighboring point is a point that is on the same plane as the points that are deemed to be on the same plane, wherein the center-of-gravity calculation step, the neighboring point search step, and the neighboring-point-on-plane deeming step are repeated in an order mentioned every time the neighboring point is detected, a plurality of points that are deemed to be on the same plane are acquired, and a top surface of the measurement target object is estimated based on the plurality of points.