To prevent a fault and a burn when in use of the device without charging water.

A heating element 2 is provided around an inner container 1 molded by an electric insulation material whose upper surface is opened and this device is composed of a control part 4 for controlling energizing to the heating element 2, an outer container 3 for covering the heating element 2, a first temperature detection element 5 for indirectly detecting a hot water temperature through the inner container 1 and a second temperature detection element 7 for detecting a heating element temperature. The control part 4 performs control so as to energize the heating element 2 when the first temperature detection element 5 is lower than a first set temperature T1, stop energizing and keep hot water inside the inner container 1 at a prescribed temperature when it is above the first set temperature T1, stop energizing to the heating element 2 when the temperature detected by the second temperature detection element 7 exceeds a forth set temperature T4 higher than T1 and perform energizing to the heating element 2 when it becomes lower than the set temperature T4.