Abstract: An ion beam generating device includes a liquid metal ion source configured to melt metal and emit an ion beam, and an extractor disposed under the liquid metal ion source and configured to extract the ion beam emitted from the liquid metal ion source. The liquid metal ion source includes a storage configured to accommodate the metal, an emitter configured to receive the metal from the storage and emit the ion beam, and a heater configured to heat the emitter or the storage. The heater is configured to directly heat the metal accommodated in the storage to melt the metal into a liquid state, and an amount of the ion beam to be extracted is controlled by a voltage difference that changes based on a distance between the emitter and the extractor.