To provide a burner apparatus for starting a pressurized fluidized bed boiler which can suppress the change in the metal temperature in an air diffuser pipe in igniting and extinguishing an oil burner, suppresses generation of the thermal stress in the air diffuser pipe, and avoid damages of appliances, and to provide its operational method.

The oil burner 47 is of two-fluid injection type, a combustion air bypass line 54 to lead a part of the pressurized air 4 flowing in a combustion air feed line 6 into a wind box 7 on the downstream side of a combustion liner 48 is provided, and dampers 50 and 55 to adjust the flow rate of the pressurized air 4 are disposed in the middle of the combustion air feed line 6 and the combustion air bypass line 54.