Disclosed herein are a fuel cell and a voltage supply method which are designed to supply power to various electric circuits in a stable manner.The fuel cell of stack structure with output terminals attached to different generating elements as mentioned above produces a potential across the output electrodes which corresponds to the number of generating cells connected in series. The output terminals are connected respectively to the potential regulators varying in the allowable voltage range and the ratio of voltage conversion. A large output voltage is obtained if the generating units are connected in series, and a large output current is obtained if the generating units are connected in parallel. Thus the fuel cell can supply an adequate amount of power in response to load operation.