PURPOSE: To improve a response of operation, by further providing a reserved fuel equipment for a combustor of a gas turbine equipment and supplying combustible gas of higher grade calorific value to the combustor from the reserved fuel equipment when a load instruction "high" is output.

CONSTITUTION: The captioned plant is equipped with a gasifying furnace 1 supplied with inflammable gas 14 obtained from coal, high pressure air 12 from a gas turbine equipment 1a and high temperature steam 13 from a steam turbine equipment 1b. Here produced fuel 11 is fed to a temperature regulating valve 17 and fuel valve 18 through a bypass passage 16 or a heat exchanger 15 to control a fuel flow in such a manner as to meet an output load of the equipment 1a. Here a reserved fuel tank 19 storing inflammable gas having a higher grade calorific value is equipped. Then if a load instruction "high" is output to the equipment 1a under a low loaded condition, a regulating valve 21 is opened, and the inflammable gas in the tank 19 is heated by a heat exchanger 20 to increase temperature and then supplied to a combustor 4.