Here, the second exposure portion P2b defining the other side of the cooling fluid passage F may correspond to a portion between the protrusion step portion 21 (see FIG. 7) formed at the edge of the second plate P2 and the protrusion step portion 21 (see FIG. 8) formed around the slit S of the second plate P2. The cooling fluid passage F may be separately formed for each accommodation space G, and the first plate P1 may be separately formed for each accommodation space G and may define a side of the cooling fluid passage F. Although the second plate P2 may not be separately formed for each accommodation space G, the second plate P2 may define one cooling fluid passage F from an edge of the second plate P2 to the slit S (the protrusion step portion 21 around the slit S) of the second plate P2 and may define another cooling fluid passage F from the slit S (the protrusion step portion 21 around the slit S) to another edge of the second plate P2. Here, each of a pair of protrusion step portions 21 (the protrusion step portions 21 adjacent to the main inner boundary portion MI) formed around the slit S may form a different cooling fluid passage F from each other. Each of the pair of protrusion step portions 21 formed around the slit S may include an upper surfaces flatly connected to each other, and the slit S between the pair of protrusion step portions 21 may provide an injection location of the sealing member for forming the third and fourth sealing portions 53 and 54.
