An electron source producing an electron beam which is highly reliable and stable even when it is externally oscillated. The electron source comprises a cathode (1) having an electron emitting section which is so connected to be interposed between top ends of two filaments (3) which are respectively connected to two conductive pins (4) provided on an insulator member (5), an end of the cathode (1) which differs from the electron emitting section being fixed to the insulator member (5), wherein the two filaments (3) are being twofold symmetry with a center on a center axis of the cathode (1), and preferably, the end of the cathode (1) which differs from the electron emitting section is fixed to the insulator member (5) via a metallic member (6) brazed to the insulator member, and more preferably, a curved portion is provided to the filaments.