PURPOSE: To improve sureness, durability and resistance to load of securing of a slit member in the grille by a method wherein the slit member is pinched and secured from both sides thereof by a pushed-and-spread part formed on an intermediate reinforcing member between neighboring slit members.

CONSTITUTION: The intermediate reinforcing member 5 between neighboring slit members 3, 3 is received and supported from the lower part thereof. When the intermediate reinforcing member 5 is pressed by an upper die 9, the opening groove section 5a thereof is spread outwardly and deforms along the receiving grooves 6,...6 of a lower die 7. In this case, the part 5b of penetrating hole of the slit member 3 is spread to the width of the penetrating hole and is brought into a forced fitting condition while the part 5c between neighboring slit sections 3, 3 is spread to the width of the receiving groove 6 and is bent stepwisely whereby the intermediate member 5 pinches and secured the slit member 3 from both sides thereof. According to this method, the securing of the slit member becomes sure and the durability thereof may be improved while the intermediate reinforcing member is deformed so as to make recess and protrusion along the whole length thereof, therefore, the rigidity thereof may be increased and the resistance to load thereof may be improved.