To easily insert/pull out supporting hardware and use a cover and the supporting hardware by being separately removed by providing the supporting hardware for standing separately from the cover and inserting the supporting hardware into a groove hole of a handle mounted at the center of the cover.

A cylindrical object to be a heat insulating material is passed through wire at a location 2 and a metallic cylindrical object to be used as weight is passed through a wire line at a location 5, before linear working is performed, and folded widths 1, 2, 3, 4 are given and folded and are fixed and fastened by welding at a location 6. A groove hole is longitudinally provided from the above in the head part of a handle provided at the center location of the upper part of a cover in a part to be one end 1 of supporting hardware and the supporting hardware is fastened and fixed on/to a screwing groove of the handle. When the cover floats due to a rise in pressure at the inside at the time of boiling and water is boiled over, the lighter part of the cover rises earlier. When tip 3, 4 parts of the supporting hardware extend over the edge frame of a device body, the cover obliquely inclines and partly opens.