The objective of the present invention is to provide an ion beam device capable of forming a nanopyramid stably having one atom at the front end of an emitter tip even when the cooling temperature is lowered in order to observe a sample with a high signal-to-noise ratio. In the present invention, the ion beam device, wherein an ion beam generated from an electric field-ionized gas ion source is irradiated onto the sample to observe or process the sample, holds the temperature of the emitter tip at a second temperature higher than a first temperature for generating the ion beam and lower than room temperature, sets the extraction voltage to a second voltage higher than the first voltage used when generating the ion beam, and causes field evaporation of atoms at the front end of the emitter tip, when forming the nanopyramid having one atom at the front end of the emitter tip.