A fuel cell system, comprising: a fuel cell that is supplied with a fuel gas and an oxidant gas to generate electric power; a fuel tank that stores therein liquid fuel acting as the fuel gas; an oxidant gas supply source configured to supply the oxidant gas; a supply/discharge mechanism that is connected to the fuel tank and the oxidant gas supply source, the supply/discharge mechanism being configured to supply and discharge the fuel gas to and from an anode of the fuel cell and being configured to supply and discharge the oxidant gas to and from a cathode of the fuel cell, wherein the supply/discharge mechanism comprises: a fuel gas supply system connected to the fuel tank and configured to supply the fuel gas to the anode of the fuel cell; an oxidant gas supply system connected to the oxidant gas supply source and configured to supply the oxidant gas to the cathode of the fuel cell; and a system discharge system configured to discharge a fuel off-gas and an oxidant off-gas discharged from the fuel cell; a collector configured to collect vaporized fuel that is vaporized in the fuel tank; an introduction path that is connected to the fuel tank and the collector, the introduction path being configured to guide the vaporized fuel to the collector; a discharge path configured to discharge the vaporized fuel collected by the collector to the supply/discharge mechanism; and a supply path and a purge gas supply unit that are connected to the collector, the supply path and the purge gas supply unit being configured to supply, to the collector, purge gas for pushing out the vaporized fuel collected by the collector into the discharge path, characterized in that the purge gas supply unit also serves as the oxidant gas supply source, the oxidant gas supply system includes a first path supplying the oxidant gas to the cathode of the fuel cell and a second path branched from the first path, the supply path and the discharge path are incorporated into the second path, and the second path is connected to at least one of: the first path at a connection position located between the first path and the second path, wherein the connection position is located further downstream in the first path than the branched position between the first path and the second path; the fuel gas supply system; or the system discharge system. a fuel cell that is supplied with a fuel gas and an oxidant gas to generate electric power; a fuel tank that stores therein liquid fuel acting as the fuel gas; an oxidant gas supply source configured to supply the oxidant gas; a supply/discharge mechanism that is connected to the fuel tank and the oxidant gas supply source, the supply/discharge mechanism being configured to supply and discharge the fuel gas to and from an anode of the fuel cell and being configured to supply and discharge the oxidant gas to and from a cathode of the fuel cell, wherein the supply/discharge mechanism comprises: a fuel gas supply system connected to the fuel tank and configured to supply the fuel gas to the anode of the fuel cell; an oxidant gas supply system connected to the oxidant gas supply source and configured to supply the oxidant gas to the cathode of the fuel cell; and a system discharge system configured to discharge a fuel off-gas and an oxidant off-gas discharged from the fuel cell; a fuel gas supply system connected to the fuel tank and configured to supply the fuel gas to the anode of the fuel cell; an oxidant gas supply system connected to the oxidant gas supply source and configured to supply the oxidant gas to the cathode of the fuel cell; and a system discharge system configured to discharge a fuel off-gas and an oxidant off-gas discharged from the fuel cell; a collector configured to collect vaporized fuel that is vaporized in the fuel tank; an introduction path that is connected to the fuel tank and the collector, the introduction path being configured to guide the vaporized fuel to the collector; a discharge path configured to discharge the vaporized fuel collected by the collector to the supply/discharge mechanism; and a supply path and a purge gas supply unit that are connected to the collector, the supply path and the purge gas supply unit being configured to supply, to the collector, purge gas for pushing out the vaporized fuel collected by the collector into the discharge path, characterized in that the purge gas supply unit also serves as the oxidant gas supply source, the oxidant gas supply system includes a first path supplying the oxidant gas to the cathode of the fuel cell and a second path branched from the first path, the supply path and the discharge path are incorporated into the second path, and the second path is connected to at least one of: the first path at a connection position located between the first path and the second path, wherein the connection position is located further downstream in the first path than the branched position between the first path and the second path; the fuel gas supply system; or the system discharge system. the first path at a connection position located between the first path and the second path, wherein the connection position is located further downstream in the first path than the branched position between the first path and the second path; the fuel gas supply system; or the system discharge system.