In at least one of flow distribution areas 35 provided on a separator 15, plurality of first projections 46 formed in a region corresponding to a first section (parted regions 32a and 32c) of a center area (including parted regions 32a through 32c) having a relatively high flow rate of a first fluid (refrigerant) are designed to have a larger diameter of a cross section than plurality of first projections 46 formed in a region corresponding to a second section (parted region 32b) of the center area having a relatively low flow rate of the first fluid. This arrangement effectively attains a substantially uniform flow rate distribution of a fluid in a fluid flow path formed on a separator, which is configured to have concavo-convex structures formed in a mutually reversed relation on two opposed sides thereof.