PURPOSE: To increase the pressure resisting strength as well as to increase the heat accumulating capacit of each container in the heat accumulating device utilizing latent heat by covering the space between chambers on the heat collecting fluid side and the load fluid side of a vaporizing liquid sealed tube with a heat insulative material.

CONSTITUTION: The heat accumulating device 1 has the heat collecting chamber 4 into the lower part of which the hat collecting fluid 6 flows and the load fluid chamber 5 into the upper part of which the load fluid 7 flows. These chambers are heat exchanged by means of a plurality of tubelike sealed containers 2 having the vaporizing liquid 3 sealed therein. This heat exchange utilizes the evaporation latent heat of the vaporizing liquid 3. In this instance, the body part between these chambers 4 and 5 is covered with the hat insulative material 12, so that the sealed container 2 can be elongated without producing any heat loss. Thus the heat accumulating capacity of each container can be increased.