To improve completion efficiency throughout the year and enable high efficiency of coal gasification power generation to be maintained.

The coal gasification power generation system is such that coal and air or oxygen is burned in a gasification furnace device 1 and coal gasification gas is generated. The coal gasification gas is then refined to clean gas with a desulphurization device 5. A gas turbine power generation device 14 is operated with the clean gas. Provided is a liquid storage means 17 that liquefies and stores clean gas during times of low load such as at night and during holidays, and a combined cycle 19 which generates power using clean gas gasified and supplied from the liquid storage means 17 during times of high load such as during peak daytime hours on weekdays. At night and during holidays when there is not much need for power, the power plant can conduct rated operation and continually highly efficient operation becomes possible. Through this it is possible to reduce the amount of coal used throughout the year.