A focused ion beam apparatus is equipped with a gas field ion source that can produce a focused ion beam for a long period of time by stably and continuously emitting ions from the gas field ion source having high luminance, along an optical axis of an ion-optical system for a long period of time. The gas field ion source has an emitter for emitting ions, the emitter having a sharpened end part made of iridium fixed to a cylinder-shaped base part made of dissimilar wire.