NOVELTY - A fuel cell system comprises fuel tank (2); a mixing tank (4) for storing fuel solution; fuel supply unit (3) for supplying fuel from tank to mixing tank; power generator (7) having membrane electrode assembly with electrolyte membrane, anode electrode and cathode electrode, generating power by reaction of fuel solution with air; fuel circulation unit (5) circulating fuel solution to anode electrode; air supply unit (6) supplying air to cathode electrode; and air supply mechanism supplying air to anode so as to discharge fuel solution from inside of anode electrode to mixing tank.    USE - As a fuel cell system (claimed).    ADVANTAGE - The fuel cell system can operate while maintaining long-term high efficiency in a liquid-type fuel cell.    DETAILED DESCRIPTION - A fuel cell system comprises a fuel tank (2) configured to store fuel; a mixing tank (4) configured to store a fuel solution diluted from the fuel; a fuel supply unit (3) configured to supply the fuel from the fuel tank to the mixing tank; a power generator (7) containing a membrane electrode assembly having an electrolyte membrane, an anode electrode and a cathode electrode, where the anode and cathode electrodes sandwich the electrolyte membrane, configured to generate power by reaction of the fuel solution supplied to the anode electrode with air supplied to the cathode electrode; a fuel circulation unit (5) configured to circulate the fuel solution from the mixing tank to the anode electrode; an air supply unit (6) configured to supply air to the cathode electrode; an air supply mechanism configured to supply air to the anode electrode so as to discharge the fuel solution from the inside of the anode electrode to the mixing tank; and a temperature adjustment unit configured to control a temperature of the power generator. The system further comprises a liquid amount detector (41) configured to detect amount of liquid in the mixing tank, where the fuel solution is discharged from the inside of the anode electrode to the mixing tank based on the amount of liquid; and a concentration detector (42) configured to detect a concentration of liquid in the mixing tank, where air is taken into the anode electrode based on the concentration of the fuel.    DESCRIPTION OF DRAWING(S) - The figure shows block diagram of fuel cell system.    Auxiliary equipment (1)    Fuel tank (2)    Fuel supply unit (3)    Mixing tank (4)    Fuel circulation unit (5)    Air supply unit (6)    Power generator (7)    Power adjustment unit (9)    Controller (10)    Liquid amount detector (41)    Concentration detector. (42)