In the present invention, when the z coordinate value of the highest point of the contour of a subject with reference to a target coordinate exceeds a height limit (S12: YES), the excess of the highest point of the contour of the subject over the height limit is subtracted from the z coordinate value of the target coordinate (S13). When the z coordinate value of the highest point of the contour of the subject with reference to the target coordinate is not higher than the height limit (S12: NO), movement of an upper plate from the current coordinate of the upper plate to the target coordinate, which has been read in S11, is equally divided into 100 movements and the trajectory of the contour of the subject is calculated for each movement (S14). When the highest point of the entire contour determined by the process of S14 is not higher than the height limit (S16: NO), the movement of the upper plate to the target coordinate is executed (S17).
