A fuel cell stack including a cell stacked body and a case having four side walls facing four side surfaces of the cell stacked body extending in a predetermined direction to form an accommodation space accommodating the cell stacked body. The side walls are configured by a substantially plate shaped member having a substantially rectangular shape. The case includes joint portions joined by friction stir welding on connection surfaces between first and second side walls, between the second and third side walls, between the third and fourth side walls and between the fourth and first side walls, respectively, and a machined portion on a first surface of the side wall facing an accommodation space.