Polymer electrolyte fuel cell and related method

A polymer electrolyte fuel cell includes an electric power generating cell provided with a fuel electrode (2), an oxidizer electrode (3), a polymer electrolyte membrane (1) sandwiched between the fuel electrode (2) and the oxidizer electrode (3) and a separator (5) formed with a gas flow passage (7) for reaction gas to be supplied to at least one of the fuel electrode and the oxidizer electrode. Also, the polymer electrolyte fuel cell includes a flow passage changeover mechanism (10,11,21,22,31,32) changing over a configuration of the gas flow passage in accordance with an operating condition of a polymer electrolyte fuel cell.