PURPOSE: To furnish an exterior plate of an automobile with a rigidity by boring long holes at regular intervals in a flange part of the exterior plate such as a bonnet, door or the like and harden fillers poured through said holes.

CONSTITUTION: Since flanges 5 have long holes 7, extended at regular intervals, along a longitudinal direction, it is possible to execute, in advance of pouring fillers, a sheet metal process including adhesion of the reinforcement 3 to an inside of an exterior plate 4 by welding and a subsequent process of painting an exterior plate 2 and the reinforcement 3 with a rust preventive primer such as an electrodeposit or the like. Fillers 10 are put into the long holes 7, 7 ... of the flanges 5, 5 by a pouring implement. Also, movement of the pouring implement along the long holes 7 effects pouring of the fillers 10 at each point of adhesion 9, 9 ... so as to evenly cover the fixed breadth with the long holes 7, 7 ... as its center.