To provide a coal gasifying composite power generation system having an excellent reducing capability of SOx concentration value in an exhaust gas.

In the coal gasifying composite power generation system comprising a coal partial oxidizing furnace 1, an oxidizing furnace 2, a desulfurizing furnace 3 for removing a sulfur component in a coal gasified gas, a gas turbine 4 supplied with the obtained gas as a fuel, and an exhaust heat recovering unit 5 for recovering exhaust heat from the exhaust gas from the turbine; a secondary desulfurizing unit 6 is disposed at a tail flow of the unit 5.