Gasket

A gasket formed by stacking three layers of an upper layer, an intermediate layer and a lower layer from an upper side toward a lower side in this order, wherein:

• a through hole passing through the three layers is formed, the intermediate layer is formed by stacking two plate materials, and a first plate material of the plate materials has a folded back part formed by being folded back so as to encompass an end part on the through hole side of a second plate material of the plate materials;
• a primary seal structure enclosing the through hole on an inner side in a radial direction of a periphery edge end on an outer side of the folded back part in the radial direction and a secondary seal structure enclosing the primary seal structure on the outer side in the radial direction of the periphery edge end are formed;
• the primary seal structure has a primary upper layer bead formed to the upper layer while protruding a top in one direction of upper and lower directions, a primary intermediate layer bead formed to the second plate material of the intermediate layer while protruding a top in the other direction opposite to the one direction and a primary lower layer bead formed to the lower layer while protruding a top in the one direction, and the primary upper layer bead, the primary intermediate layer bead and the primary lower layer bead are stacked in the upper and lower directions;
• and
• the secondary seal structure has a secondary upper layer bead formed to the upper layer while protruding a top in the one direction, a secondary intermediate layer bead formed to the second plate material while protruding a top in the other direction and a secondary lower layer bead formed to the lower layer while protruding a top in the one direction, and the secondary upper layer bead, the secondary intermediate layer bead and the secondary lower layer bead are stacked in the upper and lower directions.