Patent ID: 7247981

Claim:
An image forming apparatus comprising: a cathode substrate having plural electron emitting devices and a cathode electrode; an anode substrate positioned in an opposed relationship to said cathode substrate and having a light emitting member capable of emitting light by an irradiation with electrons emitting from said electron emitting devices, an anode electrode and a guard electrode; a plate-shaped spacer positioned between the cathode electrode and the anode electrode and between the cathode electrode and the guard electrode in contact with the cathode electrode and the anode electrode; and a frame member provided between a peripheral portion of the cathode electrode and the anode electrode and adapted to constitute a vacuum container together with the cathode substrate and the anode substrate: wherein the guard electrode is positioned between the anode electrode and the frame member, and a distance x [m] between the anode electrode and the guard electrode, a height hs [m] of the spacer, a potential Va [V] of the anode and a gap Lg [m] between the guard electrode and the spacer satisfy a following condition: ( for ⁢ ⁢ x ≤ 0.5 ⁢ ⁢ hs ) Lg ≥ [ - x hs + 0.8 ] ⁢ Va 4 × 10 8 ( 1 ) ( for ⁢ ⁢ 0.5 ⁢ hs < x ≤ hs ) Lg ≥ [ - 0.4 ⁢ x hs + 0.5 ] ⁢ Va 4 × 10 8 ( 2 ) ( for ⁢ ⁢ hs < x ) Lg ≥ 0.1 ⁢ ⁢ Va 4 × 10 8 . ( 3 )