Abstract: A method of forming a through hole, wherein a spot of a laser light scans along a predetermined path and forms a through hole includes a first process in which the spot of the laser light circulates along an inner path from a predetermined first point on the inner path and reaches a predetermined second point. The inner path is positioned at an inner side relative to an outer path. The predetermined second point is positioned before the spot of the laser light returns to the predetermined first point. The method includes a second process in which the spot of the laser light moves along a transition path and reaches a predetermined third point on the outer path. The method includes a third process in which the spot of the laser light circulates along the outer path from the predetermined third point and returns to the predetermined third point.