PURPOSE: To enable the operation of a fuel cell power generating equipment under the condition that the power generating efficiency thereof is stabilized independently of the fluctuation of power load by combining a fuel cell system and an oxidant gas storing system for use inside of a power generating equipment.

CONSTITUTION: In a gas storing system 8, air is pressurized by a high pressure air compressor 9 to a required pressure in a required time and stored in a storage tank 13. The heat generated this stage is exchanged for water by a heat exchanger 11, and recovered in a storage equipment 12 as a driving heat source for freezer or the like. The high pressure air stored in the tank 13 is fed to an expansion turbine 15, and reduced to a pressure required by a fuel cell 2, and the electric power is recovered by a generator 16. Cryogenic energy generated by this reduction of pressure is recovered by a heat exchanger 17. Thereafter, at the time of peak of demand for power, an oxidant supplying device 3 of the fuel cell system 1 is stopped, and the low-pressure air is supplied from an energy recovering means 14 to increase the power to be supplied.