A flow passage forming plate includes a plate main body, a peripheral wall, and a ledge. The plate main body has a gas path surface facing a side of a gas flow passage, and an inner surface facing the opposite side from the gas path surface. The peripheral wall protrudes along a peripheral edge of the plate main body, from the inner surface toward an opposite-flow-passage side. The ledge protrudes along an inner wall surface of the peripheral wall, from the inner surface toward the opposite-flow-passage side. The ledge receives an impingement plate having a plurality of through-holes. The ledge is disposed only in a part of an inner wall surface of the peripheral wall.