PURPOSE:To provide an electron gun for generating a large current of electron beam with nearly an uniform length. CONSTITUTION:When a negative electrode high voltage pulse is applied to a conductor 11 with conductors 12 as an earth potential, electrons are generated by creeping discharge on the anode opposite surface of an insulator 2, and electron beams are accelerated toward the anode. When the conductors 12 are provided so as to longitudinally disperse the positions to generate creeping discharge, the concentration of electron generating sources can be prevented, and nearly uniform lengthy electron beams can be provided. Capacitors 3 provided between the conductors 12 and a box body at the earth potential generate the creeping discharge independently in all the dispersedly provided creeping discharge generating parts.