The polymer electrolyte fuel cell of the present invention is equipped with a cell having an MEA having a hydrogen ion-conducting polymer electrolyte membrane and an anode and a cathode sandwiching the polymer electrolyte membrane; a platelike anode-side separator positioned on one side of the MEA so that the front surface thereof contacts the anode, with fuel gas passages through which fuel gas flows being formed in the front surface; and a platelike cathode-side separator positioned on the other side of the MEA so that the front surface thereof contacts the cathode, with oxidizing gas passages through which oxidizing gas flows being formed in the front surface; a cell stack in which a plurality of said cells is stacked; and a cooling water flow passage, through which cooling water flows, formed on at least the rear surface of one from among the anode-side separator and the cathode-side separator of at least a prescribed cell in said cell stack; where said fuel gas, oxidizing gas, and cooling water flow through said fuel gas passage, oxidizing gas passage, and cooling water passage, respectively, in a manner not running counter to gravity.