To easily inspect a degree of vacuum in an image forming device even after a making process of the image forming device and sealing of an exhaust pipe.

In an image forming device having an electron source having plural electron emitting elements 54 on a base board in an envelope, an image forming member oppositely arranged on the base board and a getter material (a nonevaporation type getter 57) for maintaining a degree of vacuum inside of the envelope, a vacuum degree detecting means is arranged to detect a degree of vacuum inside of the image forming device on the basis of a change in a resistance value of the getter material (the nonevaporation type getter 57).