A production method includes a placement step, a first pressing step, and a second pressing step. In the placement step, a blank plate is placed in press tooling. In the first pressing step, the blank plate is caused to undergo bend forming in such a way that concave ridges, a concave area, and areas of concave-correspondence vertical wall areas that are areas adjacent to the concave ridges are formed in the blank plate. In the second pressing step, the resultant plate is caused to undergo draw forming in such a way that convex ridges, a convex area, areas of convex-correspondence vertical wall areas that are areas adjacent to the convex ridges are formed in the resultant plate.