Abstract: A liquid metal ion source device for using bismuth and an alloy of the bismuth is provided. The liquid metal ion source device includes a base formed of an electrically insulating material, two electrodes connected to the base and configured to supply current, a needle mounted on the base and configured to pass through the base, a filament including a pair of connection rods connected to the two electrodes, respectively, a pair of support rods formed to be extended from the pair of connection rods, respectively, and provided in a direction away from the base and towards the needle, and a filament head connecting the pair of support rods to one another and having a shape curved toward the base, and a reservoir configured to accommodate at least a portion of the filament head inside the reservoir and store a liquid metal.