An ion beam apparatus includes an ion source configured to emit an ion beam, a condenser lens electrode that condenses the ion beam, and a condenser lens power source configured to apply a voltage to the condenser lens electrode. A storage portion stores a first voltage value, a second voltage value, a third voltage value, and a fourth voltage value. A control portion retrieves the third voltage value from the storage portion and sets the retrieved third voltage value to the condenser lens power source when an observation mode is switched to a wide-range observation mode, and retrieves the fourth voltage value from the storage portion and sets the retrieved fourth voltage value to the condenser lens power source when a processing mode is switched to the wide-range observation mode.