PURPOSE: To dissolve the extension of the production lead time by the attachment process of an exhaust tube or higher facility cost, and further to enable the cost reduction of a front vessel, and promote total cost down, in an image display element used as each kind off display.

CONSTITUTION: The shortening of production time, the reduction of facility cost, and the cost down of a front vessel can be realized by providing a U-shaped hole 5a for an exhaust pipe at the seal part of a front vessel 1, and junctioning the front vessel 1, the rear vessel 2, and the exhaust pipe 3 at the same time.