field ion source 1 ion beam irradiation system column 2 sample chamber 3 and cooling mechanism 4 herein the interiors of the gas field ion source 1 ion beam irradiation system column 2 and sample chamber constitute a vacuum chamber the constitution of the gas field ion source 1 will be detailed later in a vacuum chamber 68 an acicular emitter tip 21 and an extraction electrode 24 opposed to the emitter tip and having an opening 27 through which ions pass are incorporated in addition an ionization chamber 15 is formed in order to raise a gas pressure in the perimeter of the emitter tip further an ion source evacuation pump 12 that evacuates the vacuum chamber 68 of the gas field ion source 1 is included a valve 69 capable of performing vacuum blocking is interposed between the vacuum chamber 68 and ion source evacuation pump 12 further a vacuum chamber 71 accommodating a non evaporable getter 70 serving as a material that adsorbs a gas which should be ionized is connected to the vacuum chamber 68 of the gas field ion source 1 in addition the non evaporable getter is provided with a heating mechanism 72 and cooling mechanism 73 outside the vacuum chamber the principle of the heating mechanism is resistive heating or lamp heating and the cooling mechanism employs a.