PURPOSE: To perform temporary assembling which prevents the position deviation of panels by folding back the 2nd panel with respect to the 1st panel, joining these by hemming, and punching this joined part.

CONSTITUTION: An outer panel 4 having a folded back part 4a having been folded at nearly right angle and an inner panel 5 are superposed by placing the edge part 5a of the panel 5 along the folded back part 4a. Thence, the folded back part 4a is slightly bent in a code B direction. Next, it is completely folded back to complete hemming, whereby a joined part H is formed. This joined part H is tapped by a punch P from the folded back 4a side, by which the recess 6 extending from the folded back part 4a of the panel 4 to the panel 5 is formed and the occurrence of deviation in the panels 4, 5 is thus prevented.