To calculate pressure within an accelerating tube on the basis of the indicated pressure of an ion pump or the like and to indicate it.

This device for indicating the vacuum pressure of an electron microscope accelerating tube computes and indicates the vacuum pressure within the accelerating tube having an electron-ray source 2 at its top and having a stack of electrodes arranged in series, with gas exhausted from the lower portion of the tube. The device includes a pressure measuring means 1 for measuring pressure at an exhaust system; a pressure computing means 3 for calculating pressure within the accelerating tube using a predetermined factor and on the basis of the pressure measured by the pressure measuring means 1, the factor varying depending on whether or not the electron-beam source 2 is on or off; and an indicating means 6 for indicating the pressure calculated by the pressure computing means 3. The pressure is measured at the exhaust system and the pressure within the accelerating tube is indicated, whereby the top pressure within the accelerating tube and pressures within other portions, both of which cannot be directly measured, are determined from the measured pressure of the exhaust system and indicated.