PURPOSE: Raw materials of glass are separated into a purality of groups, each group is preheated and weighed and they are mixed at high temperatures, then fed into the melting furnace, thus saving energy and increasing the productivity.

CONSTITUTION: A part 31 of high-temperature waste combustion gas 30 is combined with a part 39 of gases coming out of preheaters 12 and 13 and introduced in parallel into preheaters 12 and 13 to heat raw material groups A and B respectively so that no eutectic reaction occurs among the components. After preheating, both of the gases are combined, mixed with a part 32 of the high-temperature gas and introduced into preheaters 11 and 14 to preheat groups C and D. The gas going out of preheaters 11 and 14 is expelled with a fan 35. The cullet that is preheated appropriately with preheater 10 is charged into the furnace. Each raw material group heated in each preheater is weighed with a weighing hopper beneath the collecting hopper and they are mixed with a mixer 15 at high temperature, then charged into the furnace with charger 16.