To accurately detect power load unbalance with real operating conditions of a combined cycle power plant.

This combined cycle power plant includes: weighting means 7 and 6 for respectively weighting outputs of a gas turbine and outputs of a steam turbine based on a function corresponding to plant operating conditions; a motor output computing means 4 for computing an output of a turbine motor by adding an output of a gas turbine and an output of a steam turbine, which are respectively weighted by the weighting means 7 and 6, to each other; a power-of-generator computing means 9 for computing power of the generator; and a deviation computing means 10 for computing a deviation between the output of the turbine motor and the power of the generator. When the deviation is a predetermined value or more, an outbreak of power load unbalance is detected.