PURPOSE: To resalize the long life of a tungsten filament and the reduction in sample contamination with the improved vacuum degrees of an electron-gun chamber and sample chamber, by arranging an unvaporization type getter pump inside an exhaust pipe linked to a vacuum pump.

CONSTITUTION: The unvaporization type getter pump is formed by stacking getter agent 20 of zirconium alloy and getter element 19 of ring-shaped getter ontainer 21 on pipe 23 voa spacer 24, and heater 26 for enabling getter element 19 to make exhaustion by heating element 19 is built inside pipe 23 (atmosphere side). By flange 29 this getter pump is fixed to flamge 29 at one terminal of exhaust pipe 9 linking pipe 15 extened to the electron-gun chamber with pipe 16 to the sample chamber, and the other terminal of pipe 9 is connected to the vacuum pump. Getter agent 20 of each getter element 19 adsorbs gas molecules by being heated up to about 400°C and are diffused inside before vacuum-exhausted, thereby improving degrees of vacuum