To prevent the deformation of a container in a sealing process, improve the reliability of sealing, and eliminate a problem on dimensions.
A power generation element is stored in a bottomed square container 3 having a step 2 protruding inward and being formed at a lower end of an opening 1 by enlarging the opening preliminarily. Next, a sealing member 10 and an insulation gasket 9 are placed on the step 2 in the container 3. Then, the sealing member 10 is caulked and fixed to the container 3 through the gasket 9. The enlarged width of the opening 1 satisfies a formula Axx>Ay where the enlarged width at the time of enlargement in the direction crossing the longitudinal direction is Ax and that at the time of enlargement in the longitudinal direction is Ay, and Ay is 30-60% of the wall thickness of the container 3.
KITATSUME HIDEAKI
TSUGA YUTAKA
