A focused ion beam apparatus includes a plasma generator having a plasma torch therein, which lets plasma flow out while being kept inside, a differential exhaust chamber that is connected to the plasma torch via the torch orifice to cause adiabatic expansion of the plasma flowing out of the plasma torch to form a supersonic flow of the plasma, a drawing orifice provided at the differential exhaust chamber at a position facing the torch orifice to draw ions from the supersonic flow of the plasma, a drawing electrode that electrostatically accelerates ions having passed through the drawing orifice to further draw ions, and an ion optical system that focuses the ions drawn from the drawing electrode and causing the ions to enter the sample by optically manipulating the ions.