PURPOSE: To suppress the pressure fluctuation in main burner header at the time of ignition by a method wherein auxiliary fuel is previously filled in each of pipings between a burner and a burner valve at the time of ignition of a boiler or the like.

CONSTITUTION: At the time of ignition, firstly on-off valves 9 for auxiliary fuel are open for the fixed period of time in order to fill auxiliary fuel in the pipings 5a, each of which is installed between the burner valve 4 and the tip of the burner 5. Secondly, the on-off valves 9 for auxiliary fuel is closed and the burner valves 4 are open in order to ignite the burners 5. In such a manner as mentioned above, because the piping 5a, which lies in the downstream side of the burner valve 4, is filled with auxiliary fuel at the opening of the burner valve 4, pressure fluctuation due to the abrupt efflux of high viscous main fuel from the tip of the burner 5 is eliminated.