an electron source includes : linear thermionic cathodes for emitting electron beams ; an electron beam lead - out electrode which is disposed substantially in a parallel relationship with the linear thermionic cathodes and is formed with apertures for passing the electron beams therethrough ; and a plurality of support members for supporting the linear thermionic cathodes each of which has a contact portion held in contact with at least a portion of the linear thermionic cathodes ; wherein each of the apertures of the elctron beam lead - out electrodes is disposed so as to confront the contact portion of the support member .