To improve thermal efficiency and convenience in use, uniformly keep warm the a low temperature, and improve the safety by providing a latent heat thermal storage material which is cylindrical and can be stacked in multi-stage, in which a material to be kept warm is placed on the upside of the cylinder or inserted in the interior.

Cylindrical polymethylpentene molded containers 2A, 2B stacked in two stages are respectively filled with latent heat thermal storage material 1 such as sodium acetate, and a heat insulating material 3 is formed by the latent heat thermal storage material 1 and the polymethylpentene molded containers 2A, 2B. The molded containers 2A, 2B of the warmer are formed in such a manner that the outside diameter is 11 cm, the height is 5 cm, the thickness (latent heat thermal storage material filling thickness) is 0.75 cm, and the container wall thickness is 1.5 mm. The warmer can be used for keeping warm a glue solution 5 after the heat insulating material 3 is heated by an electronic oven or boiling. The warmer is suitable for keeping warm drinks such as coffee, Japanese Sake, or the like and the other materials to be kept warm in addition to the glue 5, and the quantity of thermal storage material is changed or the design of an exterior material can be changed according to a purpose.