An electron gun includes: an electron source; an accelerating electrode; an extraction electrode for extracting electrons from an electron emission surface of the electron source; a suppressor electrode for suppressing emission of electrons from a side surface of the electron source; and an electron beam converging unit for converging an electron beam of thermal field emission electrons emitted from the electron emission surface by applying an electric field to the electron emission surface. The electron beam converging unit is an electrostatic lens electrode which is placed between the extraction electrode and the accelerating electrode and having an opening portion in its center. A voltage is applied to the electrostatic lens electrode to converge the electron beam.