A method for controlling operation of an electron emission source includes acquiring, while varying an emission current of an electron beam, a characteristic between a surface current of a target object at a position on the surface of the target object irradiated with the electron beam, and the emission current, calculating, based on the characteristic, first gradient values each obtained by dividing the surface current of the target object by the emission current, in a predetermined range of the emission current in the characteristic, calculating a second gradient value by dividing a surface current of the target object by an emission current in a state where the electron beam has been adjusted, and adjusting a cathode temperature to make the second gradient value in the state where the electron beam has been adjusted be in the range of the first gradient values in the predetermined range of the emission current.