An electron-beam generating device, in which a number of cold cathode elements are matrix-wired, as well as a method of driving the device, is applied to an image forming apparatus. Statistical calculations are performed in advance with regard to a required electron-beam output, and loss produced in the matrix wiring is analyzed. Drive signals are corrected by deciding optimum correction values based upon the analytical results. As a result, when rows of the matrix are driven successively row by row, the intensity of the outputted electron beams can made accurate for any driving pattern.