PURPOSE: To quickly fill water glass into the clearance of quartz sand uniformly over the whole vessel.

CONSTITUTION: A terminal plate 3A different from a terminal board having an injection port has a suction port 16 for sucking the air in a vessel formed of an insulator and two terminal boards nipping it. When water glass is injected through the injection port after quart sand is injected through the same injection port, the water glass entered through the injection plot is quickly penetrated into the clearance of quartz glass by sucking the internal air through the suction port 16 to reduce the vessel internal pressure, so that the efficiency of water glass injecting work is improved, and the water glass is also uniformly filled in the vessel.