PURPOSE: To prevent latent heat storage material from leaking outside by arranging a face seal sealed along the longitudinal direction, and the end seal sections of both sealed end sections on opening sides, of a case for forming a sheet member in the shape of a shell, and by enclosing the latent heat accumulating material in an internal section.

CONSTITUTION: A sheet member 7 with polyethylene laminated on both the surfaces of an aluminum foil is formed in the shape of a shell, and a surface A side is sealed with a face seal 8, and an opening end side on one side is sealed with an end seal section 9 and is formed in the shape of a bag. After that, in an internal section, latent heat storage material 6 is enclosed, and another opening end side is sealed with an end seal section 9 and after that, both the end seals 9 are folded on the surface A side having the face seal 8 and are formed to be doubled. As a result, the latent heat storage material 6 enclosed in the internal section can be prevented from leaking outside.