A gas turbine combustor, comprising: a combustion chamber that mixes and burns fuel and air; and a burner disposed upstream of the combustion chamber, the burner jetting fuel and air into the combustion chamber and holding flames in the chamber; wherein the burner includes a first swirler having a plurality of fuel holes and a plurality of air holes formed circumferentially of the first swirler in an alternate manner and a second swirler formed with a plurality of holes through which to jet fuel or air, wherein the second swirler is arranged over the outer circumference of the first swirler, and wherein each of the holes of the second swirler is greater in width than each of the air holes of the first swirler, wherein the gas turbine combustor is configured to use two kinds of fuel gases with different heating values, and wherein the gas turbine combustor further comprises a first fuel system that includes a first fuel flow control valve and is configured to supply a blast furnace gas having a lower heating value of the two kinds of fuel gases or a coke oven gas having a higher heating value of the two kinds of fuel gases to the holes of the first swirler, a second fuel system that includes a second fuel flow control valve and is configured to supply the blast furnace gas having a lower heating value of the two kinds of fuel gases to the fuel holes of the second swirler, a bleed air system that includes a bleed control valve and is configured to supply bleed air from a gas turbine to the holes of the second swirler; and a controller configured to control the first fuel flow control valve, the second fuel flow control valve and the bleed control valve, wherein the controller is configured to control the first fuel flow control valve, the second fuel flow control valve and the bleed control valve such that during combustion of the blast furnace gas, the blast furnace gas is jetted from the fuel holes of the first swirler and the holes of the second swirler, and control the first fuel flow control valve, the second fuel flow control valve and the bleed control valve such that during combustion of the coke oven gas, the coke oven gas is jetted from the fuel holes of the first swirler and the bleed air from the gas turbine is jetted from the holes of the second swirler. a combustion chamber that mixes and burns fuel and air; and a burner disposed upstream of the combustion chamber, the burner jetting fuel and air into the combustion chamber and holding flames in the chamber; wherein the burner includes a first swirler having a plurality of fuel holes and a plurality of air holes formed circumferentially of the first swirler in an alternate manner and a second swirler formed with a plurality of holes through which to jet fuel or air, wherein the second swirler is arranged over the outer circumference of the first swirler, and wherein each of the holes of the second swirler is greater in width than each of the air holes of the first swirler, wherein the gas turbine combustor is configured to use two kinds of fuel gases with different heating values, and wherein the gas turbine combustor further comprises a first fuel system that includes a first fuel flow control valve and is configured to supply a blast furnace gas having a lower heating value of the two kinds of fuel gases or a coke oven gas having a higher heating value of the two kinds of fuel gases to the holes of the first swirler, a second fuel system that includes a second fuel flow control valve and is configured to supply the blast furnace gas having a lower heating value of the two kinds of fuel gases to the fuel holes of the second swirler, a bleed air system that includes a bleed control valve and is configured to supply bleed air from a gas turbine to the holes of the second swirler; and a controller configured to control the first fuel flow control valve, the second fuel flow control valve and the bleed control valve, wherein the controller is configured to control the first fuel flow control valve, the second fuel flow control valve and the bleed control valve such that during combustion of the blast furnace gas, the blast furnace gas is jetted from the fuel holes of the first swirler and the holes of the second swirler, and control the first fuel flow control valve, the second fuel flow control valve and the bleed control valve such that during combustion of the coke oven gas, the coke oven gas is jetted from the fuel holes of the first swirler and the bleed air from the gas turbine is jetted from the holes of the second swirler.