To eliminate an adverse effect on the operation of a gas turbine due to the power loss of an induced draft fan caused by its inlet damper and the breakage of the damper, and attain the stop of the induced draft fan when some load is applied to part of the gas turbine by facilitating the starting operation of the gas turbine.

This induced draft fan 3 for gas turbine exhaust gas, which sucks exhaust gas from a gas turbine 1 through an exhaust gas boiler 2 and exhausts it to the outside through a smokestack 4, is provided with a pressure controller 5 that detects the total wind pressure of a gas turbine outlet from between the gas turbine 1 and the exhaust boiler 2, outputs wind pressure needed for the induced draft fan, and a rotational speed controller 6 that inputs wind pressure needed for the induced draft fan from the pressure controller 5 and controls the rotational speed of the induced draft fan 3.