A gasket comprising: a first sealing part surrounding the sealed area; and a second sealing part surrounding the sealed area and being provided external to an area surrounded by the first sealing part. When a compressive deformation ratio is defined as a ratio of a deformation amount in a height direction to pressure applied to the gasket in the height direction, in the first sealing part, the compressive deformation ratio at a section to be arranged on a first fuel cell side is greater than the compressive deformation ratio at a section to be arranged on a second fuel cell side, and in the second sealing part, the compressive deformation ratio at a section to be arranged on the second fuel cell side is greater than the compressive deformation ratio at a section to be arranged on the first fuel cell side.