The present invention enables a fuel cell to be stably started by minimizing a lack of air in a gas turbine when starting the fuel cell. This fuel cell system comprises: a gas turbine (11) having a compressor (21) and a combustor (22); a first compressed air supply line (26) that supplies compressed air (A1), which has been compressed by the compressor, to the combustor; a solid oxide fuel cell (SOFC) (13) having an air electrode and a fuel electrode; a second compressed air supply line (31) that supplies partially compressed air (A2), which has been compressed by the compressor, to the air electrode; a blower (33) that is disposed on the second compressed air supply line, and raises the pressure of the compressed air (A2); a circulation booster line (60) connecting the upstream side and downstream side of the blower in the second compressed air supply line; a control valve (61) disposed on the circulation booster line; a control valve (63) disposed between the circulation booster line in the second compressed air supply line and the SOFC; and a control device (62) that closes the control valves and opens the control valves to start the blower when starting the SOFC.