PURPOSE: To certainly seal the connection part of the flange of a container and a cover, by a method wherein the cover fitting end surface for abutment present outside the opening part of a container and the stopper surface of the cover engaged with said end surface are arranged so as to be displaced from a seal end surface in a plunger longitudinal direction.

CONSTITUTION: The flange 4 of a plunger press member 3 is clamped in a state interposed between the seal end surface 7 provided to the inside of the opening part of a container 1 receiving wax 2 and the seal surface of a cover 6, and the cover fitting end surface 9 provided outside the opening part of the container 1 and the stopper surface 10 of the cover 6 engaged with said end surface 9 are arranged so as to be displaced from the seal end surface in a plunger longitudinal direction. Therefore, the flange 4 can be compressed in such a state that the flange 4 is held at the position displaced from the cover fitting end surface 9 in the plunger longitudinal direction and, therefore, the biting of the flange 4 at the assembling time of a thermal response expansion apparatus is prevented to make it possible to certainly seal the connection part of the container 1, the flange 4 and the cover 6.