In an image forming apparatus utilizing an electron emitting device, a guard electrode for preventing a creepage discharge from an anode electrode is provided without causing an abnormal discharge with a spacer. A guard electrode positioned at a predetermined distance (x) from a metal back constituting an anode electrode is positioned at such a distance (Lg) from a spacer as not to cause a discharge according to a ratio (x/hs) of the distance x and a height (hs) of a spacer.