Fuel cell power generation system and method of controlling fuel cell power generation system

A fuel cell power generation system has inert gas supply means of supplying a particular inert gas at least to the reformer (1); and alternative gas supply means (6) of supplying an alternative gas other than the particular inert gas at least to the reformer, wherein when the operation of the fuel cell is stopped, the alternative gas supply means is used to discharge hydrogen rich gas staying at least in the reformer if the stop of the operation of the fuel cell is an ordinary stop, and the inert gas supply means is used to perform the discharge if the stop of the operation of the fuel cell is an emergency stop.