NOVELTY - The polymer electrolyte fuel cell (150) has a membrane electrode assembly (100) comprising a pair of catalyst layers (121a,122a) arranged on both sides of a solid polymer electrolyte film (110). A crack-free catalyst layer is provided contacting the electrolyte film and a catalyst layer having a crack (123a) on the thickness direction of the assembly. The catalyst layer(s) contains catalyst particles whose average particle diameter becomes larger towards the entrance side of the gas passageway to the exit side.    USE - For motor vehicles (claimed).    ADVANTAGE - The polymer electrolyte fuel cell maintains a high electric power generation capability over a long period of time. The increase of electron transfer resistance of the catalyst layer is suppressed to the minimum. The elution of catalyst particles is suppressed efficiently.    DETAILED DESCRIPTION - The polymer electrolyte fuel cell (150) has a membrane electrode assembly (100) comprising a pair of catalyst layers (121a,122a) arranged on both sides of A solid polymer electrolyte film (110) with a separator (140a) having a gas passageway (141). The catalyst layer contains electrode catalyst comprising catalyst particles supported by carbon support, and a solid polymer electrolyte. A crack-free catalyst layer is provided contacting the solid polymer electrolyte film and a catalyst layer having a crack (123a) on the thickness direction of the membrane electrode assembly. The catalyst layer(s) contains catalyst particles whose average particle diameter becomes larger towards the entrance side of the gas passageway to the exit side.    An INDEPENDENT CLAIM is included for motor vehicle mounted with the polymer electrolyte fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows the cross-section of the polymer electrolyte fuel cell.    Membrane electrode assembly (100)    Solid polymer electrolyte film (110)    Catalyst layers (121a,122a)    Crack (123a)    Separator (140a)    Gas passageway (141)    Polymer electrolyte fuel cell (150)