Abstract: This performance evaluation device comprises: an acquisition unit which acquires a sampling value of a gas turbine output and a sampling value of a steam turbine output, measured at each time during the operation of a combined cycle power generation plant that generates power using the gas turbine and the steam turbine; and an output calculation unit which obtains a plant output that is a total output of the sampling value of the gas turbine output measured at a first time and the sampling value of the steam turbine that is the steam turbine output corresponding to the gas turbine output at the first time and is measured at a second time after a predetermined delay from the first time.