Fuel cell having a plurality of independently controllable gas flow channels for varying loads

A fuel cell includes a stack of unit cells, each including: a hydrogen-ion conductive polymer electrolyte membrane; an anode and a cathode sandwiching the polymer electrolyte membrane; an anode-side conductive separator plate having a gas flow path for supplying and discharging a fuel gas to and from the anode; and a cathode-side conductive separator plate having a gas flow path for supplying and discharging an oxidant gas to and from the cathode. At least one of the anode-side and cathode-side separator plates has, in one face thereof, a plurality of independent gas flow channels, which constitute the gas flow path. When the fuel cell is operated at low load, the fuel gas or the oxidant gas is supplied to one or more of the plurality of independent gas flow channels, so that the fuel cell is capable of securing sufficient gas velocity.