The present invention provides an X-ray source. The X-ray source includes a cathode unit having a nano electron emitter; a gate unit inducing electrons to be emitted from the nano electron emitter; an anode unit disposed on the gate unit to generate X rays by a collision between the emitted electrons; and a height adjusting device connected to the cathode unit to adjust the height of the cathode unit. Thus, the position of the cathode unit can be adjusted.
