A control parameter automatic-adjustment apparatus configured to adjust a control parameter which is used when a control apparatus of a plant calculates an operational control signal, the apparatus comprising: a simulator that is configured to perform simulation analysis on performance that result when operating the plant using a control parameter, and to output a simulation measurement signal as a result of the analysis; a learning unit that is configured to search for an optimal control parameter using the simulator; and a knowledge database that is configured to store knowledge information which associates the control parameter with the simulation measurement signal, wherein the learning unit includes a search range determination unit that is configured to determine a control parameter search range based on the knowledge information that is stored in the knowledge database, and characterized in that the search range determination unit is configured to calculate, before putting the simulator into operation, a similarity between a combination of a certain control parameter and a combination of setting values for control parameters that are stored in the knowledge database, determine whether or not a similar control parameter having the similarity equal to or greater than a prescribed value is present among control parameters that are stored in the knowledge database, include, if the similar control parameter is determined not to be present, the certain control parameter within the control parameter search range, calculate, if the similar control parameter is determined to be present, a predicted value of a simulation measurement signal which would be obtained by putting the simulator into operation using the certain control parameter, using a simulation measurement signal for the similar control parameter, which simulation measurement signal being stored in the knowledge database, and reduce the control parameter search range by excluding the certain control parameter from the control parameter search range when the predicted value does not satisfy a prescribed purpose, and by including the certain control parameter within the control parameter search range when the predicted value satisfies the prescribed purpose, and wherein the learning unit is configured to search for the optimal control parameter by operating the simulator using the control parameter within the control parameter search range. a control parameter which is used when a control apparatus of a plant calculates an operational control signal, the apparatus comprising: a simulator that is configured to perform simulation analysis on performance that result when operating the plant using a control parameter, and to output a simulation measurement signal as a result of the analysis; a learning unit that is configured to search for an optimal control parameter using the simulator; and a knowledge database that is configured to store knowledge information which associates the control parameter with the simulation measurement signal, wherein the learning unit includes a search range determination unit that is configured to determine a control parameter search range based on the knowledge information that is stored in the knowledge database, and characterized in that the search range determination unit is configured to calculate, before putting the simulator into operation, a similarity between a combination of a certain control parameter and a combination of setting values for control parameters that are stored in the knowledge database, determine whether or not a similar control parameter having the similarity equal to or greater than a prescribed value is present among control parameters that are stored in the knowledge database, include, if the similar control parameter is determined not to be present, the certain control parameter within the control parameter search range, calculate, if the similar control parameter is determined to be present, a predicted value of a simulation measurement signal which would be obtained by putting the simulator into operation using the certain control parameter, using a simulation measurement signal for the similar control parameter, which simulation measurement signal being stored in the knowledge database, and reduce the control parameter search range by excluding the certain control parameter from the control parameter search range when the predicted value does not satisfy a prescribed purpose, and by including the certain control parameter within the control parameter search range when the predicted value satisfies the prescribed purpose, and wherein the learning unit is configured to search for the optimal control parameter by operating the simulator using the control parameter within the control parameter search range.