A power generation system includes a gas turbine having a compressor, a combustor, and a turbine, an inlet guide vane in an air intake port in the compressor, a first compressed air supply line for supplying compressed air compressed by the compressor to the combustor, a solid oxide fuel cell (SOFC) having an air electrode and a fuel electrode, a second compressed air supply line for supplying at least part of the compressed air compressed by the compressor to the air electrode, a control valve in the second compressed air supply line, and a control device for opening the control valve when the SOFC is activated and changing a degree of opening of the inlet guide vane from a preset reference degree of opening.