NOVELTY - A fuel cell system comprises fuel cell including electricity generation body that generates electricity while fuel gas supplied to anode is not discharged to outside but resides inside; fuel gas supply portion that supplies fuel gas to anode; oxidant gas supply portion that supplies oxidant gas to cathode; cathode off-gas discharge portion that discharges cathode off-gas to outside of cell; requested-output input portion that inputs requested output requested by load; and output control portion that controls output of fuel cell based on input requested output.    USE - A fuel cell system for use as electric power source.    ADVANTAGE - The fuel cell system includes anode dead-end type fuel cell, where output is restricted by output control portion to output that is smaller than that requested by load, thus problem caused by local residence of impurity gas in anode of electricity generation body at the time of start-up of fuel cell is restrained.    DETAILED DESCRIPTION - A fuel cell system comprises fuel cell including electricity generation body formed by joining anode to surface of electrolyte membrane and cathode to another surface of electrolyte membrane, and generates electricity while fuel gas supplied to anode is not discharged to outside but resides inside; fuel gas supply portion that supplies fuel gas to anode; oxidant gas supply portion that supplies oxidant gas containing oxygen and impurity gas other than oxygen, to cathode; cathode off-gas discharge portion that discharges cathode off-gas i.e. oxidant gas left unused for electricity generation in cathode, to outside of cell; requested-output input portion that inputs requested output requested by load; and output control portion that controls output of fuel cell based on input requested output. The output control portion controls fuel gas supply portion, oxidant gas supply portion and cathode off-gas discharge portion based on input requested output; and causes fuel gas to be supplied to anode and oxidant gas to cathode, and causes cathode off-gas to be discharged from cathode. The output control portion restricts output of fuel cell to output that is smaller than requested output at start-up time of fuel cell. An INDEPENDENT CLAIM is included for control method for fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of a flow of start-up control process of fuel cell system.    Requested output acquiring step (S100)    Output prohibiting step (S110)    Operation conditions acquiring step (S120)    Output restriction time setting step (S130)    Timer referring step (S140)