NOVELTY - The system (10) has a fuel gas flow channel (44) and an oxidizing agent gas flow path (42) equipped with multiple fuel cells (20) with counter-current flow. The fuel cells are stacked by a fuel cell stack (14) in perpendicular direction (A) in an electrode plane along horizontal direction. An attachment part (16) is attached to the fuel cell stack by inclining with respect to the horizontal direction in a state of upwardly arranging an entrance side of the fuel gas flow channel with respect to the horizontal direction rather than an exit side of the flow channel.    USE - Fuel cell system i.e. polymer electrolyte fuel cell system, for use in a fuel cell electric vehicle i.e. car.    ADVANTAGE - The attachment part is attached to the fuel cell stack by inclining with respect to the horizontal direction in the state of upwardly arranging the entrance side of the fuel gas flow channel with respect to the horizontal direction rather than the exit side of the flow channel, so that condensed water within the fuel gas flow channel is smoothly drained in a reliable manner by the exit side from the entrance side along the inclination of the fuel gas flow channel, without existing stagnant water in the fuel gas flow channel, thus maintaining favorable electric power generation, without falling stoichiometry of fuel gas. The oxidizing agent gas flow path in which pressure difference of an oxidizing agent gas inlet communicating hole side and an oxidizing agent gas outlet communicating hole side is large when flow volume of the oxidizing agent gas that circulates via the oxidizing agent gas flow path, and viscosity and density of gas are higher than flow volume of the fuel gas that circulates via the fuel gas flow channel even if the oxidizing agent gas inlet communicating hole side is arranged below rather than the oxidizing agent gas outlet communicating hole side, so that generated water in the oxidizing agent gas flow path is smoothly drained in a reliable manner by the oxidizing agent gas inlet communicating hole side from the oxidizing agent gas outlet communicating hole side using the pressure difference, thus maintaining stoichiometry of the oxidizing agent gas, without existing stagnant water in the oxidizing agent gas flow path, and performing favorable electric power generation.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a fuel cell system.'(Drawing includes non-English language text)'    Perpendicular direction (A)    Fuel cell system (10)    Fuel cell stack (14)    Attachment part (16)    Fuel cells (20)    Oxidizing agent gas flow path (42)    Fuel gas flow channel (44)