The present invention relates to an automatic water supply-type steam generator using vapor pressure for creating the optimum vacuum pressure inside a pressurized water supply tank, and for smoothly providing water to the pressurized water supply tank by using the strong aspiration force that is created by means of the vacuum pressure while continuously generating steam. The present invention is characterized by allowing control of the vacuum pressure to the optimum state when creating the vacuum pressure inside the pressurized water supply tank by introducing an adequate amount of outside air from the atmosphere through an air vent. In addition, the present invention is characterized by providing a means for cooling the pressurized water supply tank so as to control the vacuum pressure inside the tank to the optimum state.