A fuel cell stack in which a plurality of cells are stacked in a stacking direction, the fuel cell stack comprising a gasket that is disposed unbonded between separators (40, 50) of two cells of a fuel cell stack adjacent to each other in a stacking direction and seals a gap between the separators (40, 50), the gasket comprising a central sealing part that comes in close contact with the two separators (40, 50), wherein in a cross-section perpendicular to a length direction of the central sealing part, the length direction being a direction perpendicular to the stacking direction, a plane of coordinates along the cross-section is divided, by a coordinate axis extending along an X-coordinate axis and a coordinate axis extending along a Z-coordinate axis, into a first quadrant, a portion where X > 0 and Z > 0, a second quadrant, a portion where X < 0 and Z > 0, a third quadrant, a portion where X < 0 and Z < 0, and a fourth quadrant, a portion where X > 0 and Z < 0, an origin at which the X-coordinate axis and the Z-coordinate axis intersect each other coincides with a center point of the cross-section of the central sealing part, the central sealing part has an outer peripheral line within the first quadrant defined by a right angular range around the center point from 0 degree to 90 degrees relative to the stacking direction, the right angular range comprising a first angular range and a second angular range, and has an outer peripheral point that is one point on the outer peripheral line and that is located at a distance of a first length L1 from the center point, within the first angular range being a range around the center point from 0 degree towards the outer peripheral point relative to the stacking direction, each point on the outer peripheral line satisfies a relation L2 < L1, where L2 is a second length that is a distance from the center point to the respective each point, within the second angular range being a range around the center point from the outer peripheral point towards the 90 degrees relative to the stacking direction, each point on the outer peripheral line satisfies a relation L3 < L1, where L3 is a distance from the center point to the respective each point, the central sealing part includes an O-ring portion having a circular cross-sectional shape and first to fourth protrusions provided on an outer periphery of the O-ring portion respectively in the first to fourth quadrants, the outer peripheral point is an apex of the first protrusion, portions of the central sealing part in the first quadrant and the second quadrant are line-symmetrical with respect to the Z-coordinate axis, portions of the central sealing part in the first quadrant and the third quadrant are point-symmetrical with respect to the center point, and portions of the central sealing part in the first quadrant and the fourth quadrant are line-symmetrical with respect to the X-coordinate axis. in a cross-section perpendicular to a length direction of the central sealing part, the length direction being a direction perpendicular to the stacking direction, a plane of coordinates along the cross-section is divided, by a coordinate axis extending along an X-coordinate axis and a coordinate axis extending along a Z-coordinate axis, into a first quadrant, a portion where X > 0 and Z > 0, a second quadrant, a portion where X < 0 and Z > 0, a third quadrant, a portion where X < 0 and Z < 0, and a fourth quadrant, a portion where X > 0 and Z < 0, an origin at which the X-coordinate axis and the Z-coordinate axis intersect each other coincides with a center point of the cross-section of the central sealing part, the central sealing part has an outer peripheral line within the first quadrant defined by a right angular range around the center point from 0 degree to 90 degrees relative to the stacking direction, the right angular range comprising a first angular range and a second angular range, and has an outer peripheral point that is one point on the outer peripheral line and that is located at a distance of a first length L1 from the center point, within the first angular range being a range around the center point from 0 degree towards the outer peripheral point relative to the stacking direction, each point on the outer peripheral line satisfies a relation L2 < L1, where L2 is a second length that is a distance from the center point to the respective each point, within the second angular range being a range around the center point from the outer peripheral point towards the 90 degrees relative to the stacking direction, each point on the outer peripheral line satisfies a relation L3 < L1, where L3 is a distance from the center point to the respective each point, the central sealing part includes an O-ring portion having a circular cross-sectional shape and first to fourth protrusions provided on an outer periphery of the O-ring portion respectively in the first to fourth quadrants, the outer peripheral point is an apex of the first protrusion, portions of the central sealing part in the first quadrant and the second quadrant are line-symmetrical with respect to the Z-coordinate axis, portions of the central sealing part in the first quadrant and the third quadrant are point-symmetrical with respect to the center point, and portions of the central sealing part in the first quadrant and the fourth quadrant are line-symmetrical with respect to the X-coordinate axis.