PURPOSE: To prevent cracking from being generated even during long-time use and provide a hot water supplying device which does not supply red contaminated water, by providing a plurality of wavy grooves at a cylindrical part of an outer shell as well as at a cylindrical part of an inner shell.

CONSTITUTION: Even when an inner shell 1 facing a flame jetted from a burner 4 is locally heated, a plurality of wavy grooves 9 provided at a cylindrical part of an outer shell 2 as well as a cylindrical part of the inner shell 1 absorb thermal stresses and strains generated in the inner and outer shells 1 and 2, so that the thermal strains are not concentrated on respective recessed parts (A and B) of the inner and outer shells 1 and 2. Therefore, cracking at the surface of a water drum 3 can be prevented from occurring, and red contaminated water is not generated from a hot water supplying device.