A control device (100;100a;100b) for a gas turbine comprising: a target value output unit configured to output a target value equivalent to a target rotation speed (Nt) of the gas turbine; a target value deviation calculation unit configured to obtain a target value deviation (ΔNt), the target value deviation (ΔNt) being a deviation of the target value with respect to an actual rotation speed equivalent value equivalent to an actual rotation speed (Nr) of the gas turbine; a fuel equivalent value calculation unit configured to determine a fuel equivalent value equivalent to a flow rate of fuel supplied to the gas turbine in accordance with the target value deviation (ΔNt); a rotation speed variation detecting unit configured to detect a variation of the actual rotation speed (Nr) of the gas turbine; characterized in that the control device (100;100a,100b) further comprises: an upper limit deviation calculation unit configured to obtain an upper limit deviation (ΔPu), the upper limit deviation (ΔPu) being a deviation of a set upper limit output (Pu) of the gas turbine with respect to an actual output (Pr) of the gas turbine; a lower limit deviation calculation unit configured to obtain a lower limit deviation (ΔPd), the lower limit deviation (ΔPd) being a deviation of the actual output (Pr) of the gas turbine with respect to a set lower limit output (Pd) of the gas turbine; and a parameter-changing unit (140;140a;140b) configured to change any one parameter among the target value, the actual rotation speed equivalent value, and the target value deviation (ΔNt) such that the target value deviation (ΔNt) decreases in a case where the actual rotation speed equivalent value decreases and a first value (a) exceeds the upper limit deviation (ΔPu) and that the target value deviation (ΔNt) increases in a case where the actual rotation speed equivalent value increases and a third value (c) exceeds the lower limit deviation (ΔPd). a target value output unit configured to output a target value equivalent to a target rotation speed (Nt) of the gas turbine; a target value deviation calculation unit configured to obtain a target value deviation (ΔNt), the target value deviation (ΔNt) being a deviation of the target value with respect to an actual rotation speed equivalent value equivalent to an actual rotation speed (Nr) of the gas turbine; a fuel equivalent value calculation unit configured to determine a fuel equivalent value equivalent to a flow rate of fuel supplied to the gas turbine in accordance with the target value deviation (ΔNt); a rotation speed variation detecting unit configured to detect a variation of the actual rotation speed (Nr) of the gas turbine; characterized in that the control device (100;100a,100b) further comprises: an upper limit deviation calculation unit configured to obtain an upper limit deviation (ΔPu), the upper limit deviation (ΔPu) being a deviation of a set upper limit output (Pu) of the gas turbine with respect to an actual output (Pr) of the gas turbine; a lower limit deviation calculation unit configured to obtain a lower limit deviation (ΔPd), the lower limit deviation (ΔPd) being a deviation of the actual output (Pr) of the gas turbine with respect to a set lower limit output (Pd) of the gas turbine; and a parameter-changing unit (140;140a;140b) configured to change any one parameter among the target value, the actual rotation speed equivalent value, and the target value deviation (ΔNt) such that the target value deviation (ΔNt) decreases in a case where the actual rotation speed equivalent value decreases and a first value (a) exceeds the upper limit deviation (ΔPu) and that the target value deviation (ΔNt) increases in a case where the actual rotation speed equivalent value increases and a third value (c) exceeds the lower limit deviation (ΔPd). an upper limit deviation calculation unit configured to obtain an upper limit deviation (ΔPu), the upper limit deviation (ΔPu) being a deviation of a set upper limit output (Pu) of the gas turbine with respect to an actual output (Pr) of the gas turbine; a lower limit deviation calculation unit configured to obtain a lower limit deviation (ΔPd), the lower limit deviation (ΔPd) being a deviation of the actual output (Pr) of the gas turbine with respect to a set lower limit output (Pd) of the gas turbine; and a parameter-changing unit (140;140a;140b) configured to change any one parameter among the target value, the actual rotation speed equivalent value, and the target value deviation (ΔNt) such that the target value deviation (ΔNt) decreases in a case where the actual rotation speed equivalent value decreases and a first value (a) exceeds the upper limit deviation (ΔPu) and that the target value deviation (ΔNt) increases in a case where the actual rotation speed equivalent value increases and a third value (c) exceeds the lower limit deviation (ΔPd).