Provided is a fuel cell system to allow the operation state of a fuel cell system to be monitored and to allow whether there is an abnormal unit cell or not to be detected for improving lifetime. The fuel cell system comprises a stack(10) which is formed by layering a plurality of unit cells provided with a membrane electrode assembly and a bipolar plate arranged at both sides of the membrane electrode assembly; a balance of plant (BOP)(20) which comprises a fuel supply unit and an air supply unit; a control part(40) which controls the BOP; and a voltage measurement part(30) which measures the output voltage of the unit cells to send it to the control part. The voltage measurement part comprises a voltage measurement module which measures the output voltage of the unit cells; and a multiplexer which electrically connects the voltage measurement part and the bipolar plate of the unit cells by the control of the control part.
