First protruding plates (25A) and second protruding plates (25B), the first and second protruding plates (25A, 25B) belonging to the segments (22A, 22B) of first segments (22), cause gas streams, which flow into the segments (22A, 22B), to flow out of the segments (22A, 22B), respectively, while swirling each of the gas streams about a swirl axis in different directions, the swirl axis being the direction (SD) in which the gas stream flows. Then, the gas streams are caused to flow into the two segments (22C, 22D) of second segments (22), the two segments (22C, 22D) being adjacent to each other in the direction (CD) perpendicular to the direction (SD) in which the gas streams flow.