To promote desoprtion of the residual gas molecules and to reduce the gas release by electron collision by emitting electrons from an electron emitting part while applying a negative voltage to an anode part formed on a substrate during exhausting of an image display device.

The residual gas in a vessel is discharged through an exhaust pipe 109 while heating the envelop of an image forming device. A getter also degasses by external induction heating. To the ground voltage corresponding to a driving XY matrix wiring within a rear plate 100, a minus voltage is applied to an anode part 104 while evacuating an airtight vessel. A pulse voltage is also added to the element electrode of a surface electron emitting element 102 to drive it. A gas molecule 132 adsorbed near the element is repelled by an electron 135, partially forming a plasma ion 131, which is then accelerated by the minus voltage applied to the anode part 104 and collided to a phosphor 105 and the anode part 104. Further, the residual adsorbed gas is descerped from the collision part, and the pressure in the image forming device is increased.