To prevent an inner wall of an outer container from being damaged or being corroded by the damage of its alumite treated surface while preventing the corner part of the diameter-reduced part of the outer container from being damaged by the collision of the lower corner of an inner container in contact with the corner part even when putting in/out the heavy inner container, in which contents are stored, to and from the outer container.

The warmth keeping container 1 has cylindrical outer walls 5 and inner walls 4, a heat insulating member 6 is interposed between the outer walls 5 and the inner walls 4, and a cylindrical inner container 3 for storing foods is attachably and detachably housed in an outer container 2 mounting a warmth keeping heater 7 outside a diameter-reduced part 8 by reducing the diameter at the lower part of the inner walls 4. In this case, the diameter of the inner container 3 downward from a position a little higher than the upper end of the diameter reduced part 8 of the outer container 2 is reduced largely than the amount of diameter reduction at the diameter reduced part 8 of the outer container 2 in the state of housing in the outer container 2.