A separator (15) is provided with an uneven section, which has recessed sections and protruding sections reversely formed on the front and rear surfaces and forms channels for different fluids on the surfaces. The uneven section is provided with a plurality of first protruding sections (46), a plurality of second protruding sections (42) and a reinforcing section (47). The first protruding sections protrude from one surface at regular intervals. The second protruding sections protrude from the other surface at regular intervals in the region where the first protruding sections (46) are formed. The reinforcing section has a shape that connects a plurality of positions whereupon the first protruding sections (46) are to be formed with the regularity, excluding the positions where the secondprotruding sections (42) are to be formed. The reinforcing section protrudes from the one surface. Thus, a problem brought by deformation of a separator due to a pressure difference between the fluids flowing on the surfaces of the separator is suppressed.