A gas turbine control device comprising: a frequency analyzing unit for performing a frequency analysis of combustion oscillation in a combustor of a gas turbine and for splitting a result of this frequency analysis into a plurality of respective frequency bands; an inputting unit to which a process value of the gas turbine other than a fuel composition and a heat capacity of the fuel is inputted; a state grasping unit for checking a current state of operation of the gas turbine by using the result of the frequency analysis split into the respective frequency bands from the frequency analyzing unit and the process value of the gas turbine from the inputting unit a countermeasure determining unit for determining an increase or decrease in a flow rate of at least one of the fuel flow rate and an air flow rate to the combustor on the basis of the current state of operation of the gas turbine checked by the state grasping unit; and an outputting unit for outputting an operation amount corresponding to a countermeasure determined by the countermeasure determining unit, characterized in that the gas turbine control device comprises: a fuel characteristic estimating unit having a threshold for categorizing a fuel characteristic into a plurality of categories and being configured to compare this threshold with a ratio between an output of the gas turbine and a fuel flow rate of the fuel and to determine which one out of the plurality of categories the fuel characteristic of the fuel corresponds to, the state grasping unit is configured to record a history indicating a relation between the category of the fuel characteristic determined by the fuel characteristic estimating unit and combustion oscillation of the combustor, and is configured to determine a relation of the current state of operation of the gas turbine corresponding to the category of the fuel characteristic based on the history. a frequency analyzing unit for performing a frequency analysis of combustion oscillation in a combustor of a gas turbine and for splitting a result of this frequency analysis into a plurality of respective frequency bands; an inputting unit to which a process value of the gas turbine other than a fuel composition and a heat capacity of the fuel is inputted; a state grasping unit for checking a current state of operation of the gas turbine by using the result of the frequency analysis split into the respective frequency bands from the frequency analyzing unit and the process value of the gas turbine from the inputting unit a countermeasure determining unit for determining an increase or decrease in a flow rate of at least one of the fuel flow rate and an air flow rate to the combustor on the basis of the current state of operation of the gas turbine checked by the state grasping unit; and an outputting unit for outputting an operation amount corresponding to a countermeasure determined by the countermeasure determining unit, characterized in that the gas turbine control device comprises: a fuel characteristic estimating unit having a threshold for categorizing a fuel characteristic into a plurality of categories and being configured to compare this threshold with a ratio between an output of the gas turbine and a fuel flow rate of the fuel and to determine which one out of the plurality of categories the fuel characteristic of the fuel corresponds to, the state grasping unit is configured to record a history indicating a relation between the category of the fuel characteristic determined by the fuel characteristic estimating unit and combustion oscillation of the combustor, and is configured to determine a relation of the current state of operation of the gas turbine corresponding to the category of the fuel characteristic based on the history.