A fuel cell stack configured by stacking a plurality of modules, comprising. a first module (10A, 10C); a second module (10B, 10D), placed adjacent to one surface of the first module via a first sealing member; and a third module (10B, 10D) placed adjacent to the other surface of the first module via a second sealing member; wherein the first module, the second module and the third module respectively have one or more fuel cells, each fuel cell including an electrolyte membrane, an anode, a cathode and a pair of separators placed across the electrolyte membrane, the anode and the cathode, the electrolyte membrane, the anode and the cathode being sandwiched between the pair of separators, characterized in that: the first sealing member has greater peel strength to the separator of the first module (10A, 10C) than peel strength to the separator of the second module (10B, 10D), the second sealing member has greater peel strength to the separator of the first module (10A, 10C) than peel strength to the separator of the third module (10B, 10D), a contact area of the first sealing member against the first module (10A, 10C) is greater than a contact area of the first sealing member against the second module (10B, 10D), and a contact area of the second sealing member against the first module is greater than a contact area of the second sealing member against the third module (10B, 10D). a first module (10A, 10C); a second module (10B, 10D), placed adjacent to one surface of the first module via a first sealing member; and a third module (10B, 10D) placed adjacent to the other surface of the first module via a second sealing member; wherein the first module, the second module and the third module respectively have one or more fuel cells, each fuel cell including an electrolyte membrane, an anode, a cathode and a pair of separators placed across the electrolyte membrane, the anode and the cathode, the electrolyte membrane, the anode and the cathode being sandwiched between the pair of separators, characterized in that: the first sealing member has greater peel strength to the separator of the first module (10A, 10C) than peel strength to the separator of the second module (10B, 10D), the second sealing member has greater peel strength to the separator of the first module (10A, 10C) than peel strength to the separator of the third module (10B, 10D), a contact area of the first sealing member against the first module (10A, 10C) is greater than a contact area of the first sealing member against the second module (10B, 10D), and a contact area of the second sealing member against the first module is greater than a contact area of the second sealing member against the third module (10B, 10D). the first sealing member has greater peel strength to the separator of the first module (10A, 10C) than peel strength to the separator of the second module (10B, 10D), the second sealing member has greater peel strength to the separator of the first module (10A, 10C) than peel strength to the separator of the third module (10B, 10D), a contact area of the first sealing member against the first module (10A, 10C) is greater than a contact area of the first sealing member against the second module (10B, 10D), and a contact area of the second sealing member against the first module is greater than a contact area of the second sealing member against the third module (10B, 10D).