Method for detecting possible structural deficiencies of a polymer electrolyte fuel cell

To realize a polymer electrolyte fuel cell with an increased level of safety by providing a method for easily and accurately detecting a cross leak or a micro short-circuit resulting from the initial failure or the deterioration of durability, specifically, by providing a method for operating a polymer electrolyte fuel cell comprising a stack of unit cells, each of the cells comprising a polymer electrolyte membrane, a pair of electrodes sandwiching the polymer electrolyte membrane, and electroconductive separators, which generates electricity with the supply of a fuel gas containing hydrogen to one of the electrodes and an oxidant gas containing oxygen to the other of the electrodes, in which an electric output of a single cell or a group of cells is checked after the stoppage of the supply of the fuel and oxidant gases to detect a defective cell or a defective group of cells in the fuel cell.