PURPOSE: To reduce the consumption volume of a fuel needed for steam reformation, and increase hydrogen concentration in a gas fuel by using air, which is made to be rich in oxygen by means of a transmission film which selectively transmits oxygen.

CONSTITUTION: Oxygen-rich air produced with an oxygen-rich-air producer 2, which is equipped with a transmission film 4 selectively transmitting oxygen, is induced by an induction blower 13, and supplied into a burner 7 through a pipe path 14 equipped with a control valve 15. A fuel such as town gas is supplied from a fuel supply source 16 through a pipe path 17 into a burner 7. In the burner 7, since oxygen concentration in combustion air is relatively high, a relatively high temperature can be achieved with a relatively small amount of the fuel, and the consumption volume of the fuel is reduced. In addition, since a catalyst 5 can be maintained at a relatively high temperature, reaction is accelerated due to the high temperature of the catalyst, and a gas fuel with an increased hydrogen concentration can be obtained. The gas fuel reformed within a tube 6 is supplied into a fuel cell 1 through a pipe path 18.