PURPOSE: To prepare a plate molded article at a low cost in high yield, without using a grinding step, by cooling a melt in a crucible having a polygonal orifice provided at the bottom to such a temperature as to give a suitable viscosity coefficient, and drawing down the melt through the orifice.

CONSTITUTION: A crucible 4 having a tetragonal orifice 3 at the bottom thereof is placed in an electric furnace 1 having a heating element 2, and quartz glass as a melt is contained in the crucible 4. The melt is then heated to a temperature higher than the operating temperature to refine the melt. When bubbles, cords, etc. disappear in the glass, the melt emerging from the orifice 3 is cooled to 104W107 poises viscosity coefficient within the operating temperature range. The melt emerging from the orifice 3 is then drawn down to prepare a plate molded article 5, which is then annealed and cut to prepare a plate.