A fuel system with a high power generation efficiency in which drive means can be reduced in size. The fuel cell system of the present invention is equipped with a fuel cell (FC) for generating power by circulating a fuel gas and comprises a circulation route (R) for circulating the fuel gas, drive means (PM) provided in the circulation route (R) and serving to circulate the fuel gas, and pressure regulating means (RG) for regulating the pressure of the fuel gas in the circulatory route (R). A drive characteristic of the drive means (PM) is determined based on the generated power required for the fuel cell, and the pressure regulation quantity of the pressure regulating means (RG) is determined to make up the deficiency of the drive quantity based on the determined drive characteristic of the drive means (PM).