A flow passage structure is provided with a fluid flow passage that includes a plurality of straight flow passages, a first return bend that connects the downstream end of the straight flow passage through which a fluid flows from a second end surface toward a first end surface among the plurality of straight flow passages to the upstream end of the straight flow passage which is disposed at the downstream side of the straight flow passage and is adjacent to the straight flow passage, and a second return bend that connects the downstream end of the straight flow passage through which the fluid flows from the first end surface toward the second end surface among the plurality of straight flow passages to the upstream end of the straight flow passage which is disposed at the downstream side of the straight flow passage and is adjacent to the straight flow passage.