Disclosed is an X-ray source, including: a cathode; an anode positioned on the cathode so as to face the cathode; emitters formed on the cathode; a gate electrode positioned between the cathode and the anode and including openings at positions corresponding to those of the emitters; an insulating spacer formed between the gate and the anode; and a coating layer formed on an internal wall of the insulating spacer, and including a material having a lower secondary electron emission coefficient than that of the insulating spacer.