CASING UNIT SUCH AS HOT WATER STORAGE TANK UNIT

PROBLEM TO BE SOLVED: To provide a casing unit having a structure which achieves both of protection of an incorporated heavy-weight material and prevention of breakage or deformation of a casing itself when an impact load is applied to the casing unit.SOLUTION: The hot water storage tank unit 1 incorporating a hot water storage tank 2 includes: a sheet-like upper casing 3a with which the upper part of the hot water storage tank 2 is covered; a sheet-like lateral part casing 3b with which the lateral part of the hot water storage tank 2 is covered; and a lower casing 3c to which the hot water storage tank is fixed and with which the lower part of the hot water storage tank 2 is covered. Further, the hot water storage tank unit 1 includes a cushioning material 5 disposed between the hot water storage tank 2 and the upper casing 3a, and a stress-relaxation structure which relaxes a stress which acts on a fixation part between the lateral part casing 3b and the lower part casing 3c when the impact load is applied to the hot water tank unit 1.