Abstract: It is an object to solve a bypass line corrosion problem effectively, enable prompt supply of a fuel gas into a bypass line in the event of an emergency, and provide an inexpensive coal gasification plant. An integrated coal gasification combined cycle power generation plant includes a coal gasification furnace, a dust remover, a gas refiner, a gas turbine and the like, a main system line connecting therebetween, and a bypass line connecting between the outlet side of the coal gasification furnace in the main system line and a flare stack, wherein a dust remover bypass valve which is disposed in an upstream portion of the bypass line and which opens and closes the bypass line, a treatment gas control valve which is disposed in a downstream portion of the bypass line and which controls the flow rate, and a first inert gas input line which is disposed downstream from the dust remover bypass valve and which supplies the inert gas to the bypass line are provided.