The present invention aims to enable point cloud data that uses relative coordinates and was obtained by a 3D laser scanner to be superimposed on point cloud data that uses absolute coordinates, even there is an error in the 3D laser scanner distance measurement.　The present invention is a 3D point cloud coordinate conversion device that: obtains first and second point cloud data that use relative coordinates centered on first and second origin points; obtains absolute coordinates for the first and second origin points; specifies a measurement object reference point included in both the first and second point cloud data; specifies contact points for a circle that has the distances between the reference point and the first and second origin points, respectively, as the radius thereof, by changing at least either the first or second distance; specifies a rotation angle that converts the first and second point cloud data to absolute coordinates, on the basis of three points, namely, the contact point, the first or second origin point, and the reference point for the measurement object; and rotates the first and second point cloud data.