Provided are a method and an apparatus of controlling a flow rate of a primary recirculating exhaust gas in an oxyfuel combustion boiler, capable of realizing a stable combustion by a burner in oxyfuel combustion. Weight ratio of flow rate of primary recirculating exhaust gas [ton/h] to amount of pulverized coal from a mill [ton/h] is defined as G/C, and the flow rate of primary recirculating exhaust gas is controlled so that the G/C falls within a given range.