To improve the sealing performance regardless of the magnetic force of a magnet by giving a gasket flexibility.

A gasket 22 for being attached at a heat insulation door comprises an attaching part 23, a bag-like part 25 accommodating a magnet 24 being in contact with a front face of a heat insulation box body, an expandable outer side buffering part 27 and an expandable center buffering part 28 coupling the bag-like part 25 and the attaching part 23 so as to form a first space, and a coupling piece 30 extending from the vicinity of the inner end of the attaching part 23 to the inner wall side of the bag-like part 25 so as to form a second space between the attaching part 23 and the bag-like part 25 and the center buffering part 28. The wall thicknesses of the outer side buffering part 27 and the center buffering part 28 are made thick toward the vicinity of the bag-like part 25 side between the attaching part 23 and the bag-like part 25, and the center buffering part 28 is formed into an S-shape.