Separators (5A, 5B, 6) and membrane-electrode assemblies (2) of a fuel cell stack (1) are alternately stacked in a guide box (40). The separators (5A, 5B, 6) each have groove-like gas paths (10A, 10B). Powder of an adhesive agent (7) is adhered in advance to the surfaces of the separators (5A, 5B, 6), except the gas paths (10A, 10B), through photosensitive drums (31A, 31B) to which the powder is adsorbed in a given pattern. The separators (5A, 5B, 6) and the membrane-electrode assemblies (2), stacked in the guide box (40), are heated and compressed by a press (43) and heaters (40C) to obtain a unitized fuel cell stack (1).