Whether or not workpieces are present in a workpiece storage area is determined based on an image acquired by image capturing. When the workpieces are determined to be present, whether or not a crossing part is present in the workpiece storage area is determined based on the image, the crossing part being a part where soft body portions of a plurality of workpieces cross each other in an overlapping manner. When the crossing part is determined to be present, an uppermost soft body portion placed at an uppermost position among the soft body portions crossing each other is determined based on the image. A workpiece including the uppermost soft body portion thus determined is determined as an uppermost workpiece placed at an uppermost position.