PURPOSE: To efficiently recover waste heat and to sufficiently suppress stone by heat-exchanging the waste heat of a glass smelting furnace with gas to heat and by controlling the temp. for pre-heating glass raw material batch with the heated gas.

CONSTITUTION: The glass raw material contg. soda ash and carbonaceous material such as carbon is thrown into the glass smelting furnace 1 equipped with regenerators 2A and 2B through a hopper 4 and a port 3 for throwing the batch, and molten at a high temp. Then, the exhaust gas from the regenerator 2A and 2B is introduced to a heat exchanger 7 through transportation pipes 6A and 6B to heat outside air blown into the heat exchanger 7 through a device 8 for blowing in the outside air by heat-exchanging, and thereafter, the heated air is sent to a pre-heating device 5 after mixing with outside air through a damper 9 for mixing the outside air to pre-heat the glass raw material batch at ≤420°C. On the other hand, the glass raw material batch molten in the smelting furnace 1 is discharged through a clarification vessel 10, apparatuses 11A and 11B for forming plate glass and a slowly cooling furnace 12A and 12B.