PURPOSE: To reduce the deviation of the temp. of a skelp in the starting up period of a continuous type heating furnace.
CONSTITUTION: When the heating furnace starts up the operation, fuel gas is supplied into the heating furnace 2 at the initial gas flow rate higher than the stable condition and the skelp 1 is passed through the heating furnace at the initial carrying speed lower than the stable condition. A process data treating part 5 observes the signals from a speed sensor 3 and a temp. sensor 4, and while gradually increasing the carrying speed toward a target carrying speed by an acceleration ΔV, the gas flow rate Qi is gradually lowered. Until the temps. Tin, Tij detected by the temp. sensor 4 reaches the target skelp temp., the carrying speed and the gas flow rate at this time are kept, and at the time of reaching the target skelp temp., the carrying speed is increased by acceleration ΔV and the gas flow rate is lowered. Thus, while preventing the local variation of the skelp temp. caused by lowering of the gas flow rate and excess increasing of the carrying speed during starting up the operation, the furnace can quickly started up.