A front substrate and a rear substrate are laid on each other with a
sealing frit therebetween. The front substrate, the rear substrate and the
sealing frit are heated in a chamber and impurity gas is exhausted from
both of the substrates by lowering internal pressure of the chamber. The
sealing frit is melted in the chamber by further heating the front
substrate, the rear substrate and the sealing frit. The sealing frit is
solidified in the chamber and sealing up the front substrate and the rear
substrate.
