A liquid metal ion source has a reservoir which holds a source material to-be-ionized in a melted state; an emitter which emits from its tip, ions of the melted source material fed from the reservoir; and an extracting electrode which applies a high electric field to the tip of the emitter, thereby to extract the ions from the tip of the emitter. The liquid metal ion source further comprises tank means for storing the source material to be fed to the reservoir, transfer means for transferring the source material from the tank means to the reservoir, and a vacuum chamber for holding the constituents in a vacuum state.