To fluidize bottom metal in a short time.

At a bottom part of an electric type ash melting furnace, an air cooling jacket 13 is provided to cover the lower surface side of a bottom electrode 5 to be connected to a fan 18 through an air feed line 19 with a flow regulating valve 20, so that air is sent into the air cooling jacket 13 to indirectly cool the bottom metal 11 through air cooling to the bottom electrode 5. By solidifying the bottom metal 11, the bottom electrode 5 is protected. A temperature detector 21 to detect temperature of the bottom metal 11 through temperature detection to the bottom electrode 5 is installed on the bottom electrode 5. A control device 22 is provided to control the flow regulating valve 20 to open till temperature of the bottom metal 11 detected by the temperature detector 21 becomes fluidization temperature. For fluidizing the bottom metal 11, the flow regulating valve 20 is throttled by the control device 22 to reduce air feed quantity to the air cooling jacket 13. Indirect cooling ability to the bottom metal 11 through the bottom electrode 5 is thus reduced.