To provide an operation method of a waste gasifying melting furnace that ensures a stabilized operation, and the extended range of a processing amount of waste, and hence is easily operated irrespective of skills.

When a dome-shaped melting zone M formed into a inverted truncated cone section 12 or a cylindrical section 13 in a waste gasifying melting furnace 1 is adapted to have its diameter D, a total blowing gas flow rate Q of auxiliary fuel gas such as LPG blown into a combustion gas blowing furnace 14 and oxygen or oxygen rich air mixed in a predetermined ratio is controlled to keep a predetermined amount proportional to the 2.5th power of D. Hereby, the operation is achieved such that the position of the dome- shaped melting zone M is not instable.