To inexpensively perform manufacture by folding the edge of a plate material after prescribed processing is executed on the plate material, and forming the receiving plate of a sluice gate door.

An outside is sheared into a rectangle by shearing an iron plate or the like to form a receiving plate 13. An opening 31 such as a rectangle, a square and a circle is sheared by laser processing by matching the opening of a water passage downward of the substantial center of the receiving plate 13. A corner of substantially 90 degrees is possessed on the intersection point of a side edge folding line 33 and a lower edge folding line 34 on both the ends of the receiving plate 13, and a notch part 32 having a side coinciding with the folding lines 33, 34 is provided by laser processing. Holes 37, 38 for fixing an attaching fitting by bolts are provided on both the sides of the opening 31 by laser processing. Furthermore, after a side part and a lower side part are folded along the folding lines 33, 34 by a folding machine, they are welded along the projection part of a lower side. Thereby it can be manufactured inexpensively.