A polymer electrolyte fuel cell comprising: a unit cell including a membrane-electrode assembly and a pair of plate-shaped separators (4A, 4C) provided so as to contact the membrane-electrode assembly, the membrane-electrode assembly including a polymer electrolyte membrane and a pair of electrodes (2A, 2C) sandwiching the polymer electrolyte membrane, groove-shaped gas channels (6, 7) through which reactant gases respectively flow being respectively formed on main surfaces of the electrodes or main surfaces of the separators; manifolds formed so as to respectively communicate with inlet portions of the gas channels; a gas introducing member including a gas introducing port, a gas lead-out port, and a first gas passage formed such that the gas introducing port and the gas lead-out port communicate with each other; and a first member including a main surface on which a communication portion is formed, wherein: a recess is formed at the gas lead-out port side of the gas introducing member so as to be connected to the gas lead-out port; the first member is provided such that the communication portion communicates with one of the manifolds; characterized in that the gas introducing member is provided such that the recess communicates with the communication portion, and when viewed from a thickness direction of the polymer electrolyte membrane, the gas lead-out port, the main surface of the first member, and the one manifold overlap each other; a second gas passage is constituted by the recess of the gas introducing member and the main surface of the first member; the inlet portions of the gas channels of the separators are formed such that the reactant gases flow in a vertical direction; and when viewed from the thickness direction of the polymer electrolyte membrane, the communication portion of the first member is provided in a region where the gas introducing member is provided, other than a region defined by projecting the inlet portion of the gas channel of the separator in a vertically upper direction. a unit cell including a membrane-electrode assembly and a pair of plate-shaped separators (4A, 4C) provided so as to contact the membrane-electrode assembly, the membrane-electrode assembly including a polymer electrolyte membrane and a pair of electrodes (2A, 2C) sandwiching the polymer electrolyte membrane, groove-shaped gas channels (6, 7) through which reactant gases respectively flow being respectively formed on main surfaces of the electrodes or main surfaces of the separators; manifolds formed so as to respectively communicate with inlet portions of the gas channels; a gas introducing member including a gas introducing port, a gas lead-out port, and a first gas passage formed such that the gas introducing port and the gas lead-out port communicate with each other; and a first member including a main surface on which a communication portion is formed, wherein: a recess is formed at the gas lead-out port side of the gas introducing member so as to be connected to the gas lead-out port; the first member is provided such that the communication portion communicates with one of the manifolds; a recess is formed at the gas lead-out port side of the gas introducing member so as to be connected to the gas lead-out port; the first member is provided such that the communication portion communicates with one of the manifolds;