To provide a combustion air quantity control device for a pressure fluidized bed boiler, capable of alleviating a burden on monitoring and adjusting by an operator.

A combustion air quantity control device 100 for pressure fluidized bed boilers 10, 20 includes an air-fuel ratio master 110 which controls a combustion air quantity for the pressure fluidized bed boilers 10, 20 on the basis of a load command, a fuel flow, and a furnace outlet oxygen concentration; and a monitoring device 120 which calculates an appropriate combustion air quantity for the pressure fluidized bed boilers 10, 20 and monitors whether the combustion air quantity is within a range of the appropriate combustion air quantity. When the air-fuel ratio master 110 receives a combustion air quantity abnormal signal from the monitoring device 120, the air-fuel ratio master 110 excludes the furnace outlet oxygen concentration, and controls the combustion air quantity on the basis of the load command and the fuel flow.