PURPOSE: To reduce a power consumption and get a superior heat radiation by a method wherein a liquid fuel is vapourized by a burner main body heated by a heater and then the fuel is combustioned, a process for applying electrical energy for the heater is controlled in response to a rate of operation in the burner main body.

CONSTITUTION: When the operation switch 23 is turned on, the heater 4 is energized by an electricity to heat the burner main body 1. When a temperature of the burner is reached to a desired value, the thermostat 14 is changed over to a contact point 14a. Thereby, when the burner main body 1 is started to operate through a hot water temperature thermostat 19 and at the same time the relay 25 is energized to close the contact point 27. Then, when a hot water temperature is increased and the hot water thermostat 19 is opened, the burner main body 1 is terminated and the relay 25 is deenergized. In this case, if heat radiation amount at the load part is reduced and a duration of closed time of the contact point 19b is extended over an operation period of time of the main body 1, the transistor 29 is turned on, the relay contact point 24 is changed over to a contact point 24a so as to interrupt an energization of the heater 4.