A correction electron optical system (3) has substrates in which apertures for constituting electron lenses are formed. Valves (14) whose opening degrees can be adjusted are used to relax the pressure difference between the upper and lower surfaces of each substrate caused when supply/exhaust pumps (51-56) adjust the internal pressure of a main body cover (80). The opening degrees are controlled based on outputs from differential pressure sensors (13). The pressure sensors (13) can be replaced with photosensors.