To melt a matter to be molten effectively with less energy consumption and to tap the layer of molten metals smoothly and stably without the large energy consumption in an electric melting furnace for effecting melting treatment of ashes.

The electric melting furnace 4 comprises a part of a furnace wall above a molten slag layer B1 made of a refractory wall structure 35 and a water cooled jacket 9 and a part of the furnace wall below the molten slag layer B1 made of the refractory wall structure 35 and an air cooled jacket 8. The air cooled jacket 8 is partitioned into a plurality of partitions in the circumferential direction of the melting furnace 4, the volume of the cooling air fed to the air cooled jacket 8 near a tap hole 14 starts to be reduced from a predetermined time T1 before the start of the tapping of a molten metal layer B2, the temperature of cooling air C is raised to a set temperature of ta2, the input power to the melting furnace 4 is increased at the predetermined time before the start of the tapping and the set temperature of the molten metal layer B2 is raised to the set temperature of tm2.