A gas turbine control device for a gas turbine system which comprises a combustor for generating combustion gas; a turbine having a rotor to be rotated by the combustion gas; and a power generator to be driven by the rotation of the rotor, the device comprising: a sensing unit for measuring the rotor speed and an output of the power generator; a speed regulation rate setting unit for calculating an actual speed regulation rate (δ r) based on the measured rotor speed and the measured output of the power generator, and for setting a reference speed regulation rate (δ ref) based on the actual speed regulation rate and a target speed regulation rate (δ t); and a fuel amount control unit for controlling an amount of fuel supplied to the combustor based on the set reference speed regulation rate; wherein the fuel amount control unit is configured to control the amount of fuel supplied to the combustor, by determining an output to be produced in the power generator based on the measured rotor speed and the set reference speed regulation rate; and wherein the speed regulation rate setting unit is configured to set the reference speed regulation rate so that the difference between the output of the power generator obtained by the reference speed regulation rate (δ ref) and the output of the power generator obtained by the reference speed regulation rate (δ oref) during a previous period matches with the difference between the output of the power generator obtained by the target speed regulation rate (δ t) and the output of the power generator obtained by the actual speed regulation rate (δ r); and wherein the fuel amount control unit is configured to determine the output to be produced in the power generator according to P c = P o + P N δ ref × N o − N c N N where N N denotes a rated rotor speed of the turbine, N o denotes the rotor speed at a previous reference speed regulation rate, N c denotes a current rotor speed, P N denotes a rated output of the power generator, P o denotes the power generator output at the previous reference speed regulation rate, and δ ref denotes the set reference speed regulation rate. a sensing unit for measuring the rotor speed and an output of the power generator; a speed regulation rate setting unit for calculating an actual speed regulation rate (δ r) based on the measured rotor speed and the measured output of the power generator, and for setting a reference speed regulation rate (δ ref) based on the actual speed regulation rate and a target speed regulation rate (δ t); and a fuel amount control unit for controlling an amount of fuel supplied to the combustor based on the set reference speed regulation rate; wherein the fuel amount control unit is configured to control the amount of fuel supplied to the combustor, by determining an output to be produced in the power generator based on the measured rotor speed and the set reference speed regulation rate; and wherein the speed regulation rate setting unit is configured to set the reference speed regulation rate so that the difference between the output of the power generator obtained by the reference speed regulation rate (δ ref) and the output of the power generator obtained by the reference speed regulation rate (δ oref) during a previous period matches with the difference between the output of the power generator obtained by the target speed regulation rate (δ t) and the output of the power generator obtained by the actual speed regulation rate (δ r); and wherein the fuel amount control unit is configured to determine the output to be produced in the power generator according to P c = P o + P N δ ref × N o − N c N N where N N denotes a rated rotor speed of the turbine, N o denotes the rotor speed at a previous reference speed regulation rate, N c denotes a current rotor speed, P N denotes a rated output of the power generator, P o denotes the power generator output at the previous reference speed regulation rate, and δ ref denotes the set reference speed regulation rate.