To prevent a microscopic leakage from being produced in a completed product, by minimizing the number of sealing times and a size change, in a manufacturing method of an image forming device in which a front plate, a back plate, a supporting frame and a spacer are sealed by frit glass.

In this manufacturing method, after a front plate 1 and a spacer 4 are jointed at a temperature of θ1 by frit glass having a softening temperature of β1, an entire body is sealed at a temperature of θ2(<θ1) by using frit glass having a softening temperature of β2(<β1) between a back plate 2 and the spacer 4, and by using frit glass having a softening temperature of β3(≤β2) between a supporting frame 3 and the front plate 1 and between the supporting frame and the back plate.