Provided is an X-ray generator including a thermal electron emission type X-ray generator configured to generate a negative high voltage and a filament current, a field electron emission type X-ray generator including an anode electrode to be grounded, and configured to use the negative high voltage to bias the cathode electrode, and a field emission current control unit configured to convert the filament current to generate an output voltage to be provided to a gate electrode of the field electron emission type X-ray generator and convert the filament current to fix, to a specific level, a level of an emission current flowing through the cathode electrode.