A polymer electrolyte fuel cell for supplying low-level humidified reactant gases to an upstream region of a fuel gas channel and to an upstream region of an oxidizing gas channel, respectively, the fuel cell comprising: an electrolyte layer-electrode assembly including an anode having an anode catalyst layer and an anode gas diffusion layer formed on the anode catalyst layer; a cathode having a cathode catalyst layer and a cathode gas diffusion layer formed on the cathode catalyst layer; and an electrolyte layer sandwiched between the anode and the cathode; an anode separator which has a plate shape and is provided with the fuel gas channel on one of main surfaces thereof; and a cathode separator which has a plate shape and is provided with the oxidizing gas channel on one of main surfaces thereof; wherein the electrolyte layer-electrode assembly is sandwiched between the main surface of the anode separator on which the fuel gas channel is provided and the main surface of the cathode separator on which the oxidizing gas channel is provided; a level of hydrophilicity of a cathode gas diffusion layer upstream section of the cathode gas diffusion layer which is opposite to the upstream region of the oxidizing gas channel including a mostupstream region thereof is set lower than a level of hydrophilicity of an anode gas diffusion layer opposite section of the anode gas diffusion layer which is opposite to the cathode gas diffusion layer upstream section by making the level of hydrophilicity of an entire region of the anode gas diffusion layer opposite section higher than the level of hydrophilicity of the cathode gas diffusion layer upstream section, and wherein a level of hydrophilicity of an entire region of a cathode gas diffusion layer downstream section of the cathode gas diffusion layer is set higher than a level of hydrophilicity of an anode gas diffusion layer opposite section of the anode gas diffusion layer which is opposite to the cathode gas diffusion layer downstream section. an electrolyte layer-electrode assembly including an anode having an anode catalyst layer and an anode gas diffusion layer formed on the anode catalyst layer; a cathode having a cathode catalyst layer and a cathode gas diffusion layer formed on the cathode catalyst layer; and an electrolyte layer sandwiched between the anode and the cathode; an anode separator which has a plate shape and is provided with the fuel gas channel on one of main surfaces thereof; and a cathode separator which has a plate shape and is provided with the oxidizing gas channel on one of main surfaces thereof; wherein the electrolyte layer-electrode assembly is sandwiched between the main surface of the anode separator on which the fuel gas channel is provided and the main surface of the cathode separator on which the oxidizing gas channel is provided; a level of hydrophilicity of a cathode gas diffusion layer upstream section of the cathode gas diffusion layer which is opposite to the upstream region of the oxidizing gas channel including a mostupstream region thereof is set lower than a level of hydrophilicity of an anode gas diffusion layer opposite section of the anode gas diffusion layer which is opposite to the cathode gas diffusion layer upstream section by making the level of hydrophilicity of an entire region of the anode gas diffusion layer opposite section higher than the level of hydrophilicity of the cathode gas diffusion layer upstream section, and wherein a level of hydrophilicity of an entire region of a cathode gas diffusion layer downstream section of the cathode gas diffusion layer is set higher than a level of hydrophilicity of an anode gas diffusion layer opposite section of the anode gas diffusion layer which is opposite to the cathode gas diffusion layer downstream section.