A controller of an air-conditioning system includes a feedback control unit configured to generate a state quantity command from a control parameter and a difference between a target value of a room temperature and a measured room temperature and control the room temperature to the target value on the basis of the state quantity command, a control target heat characteristic model calculation unit configured to calculate a parameter of a model regarding a heat characteristic of a control target from at least a state quantity regarding an amount of heat supplied to the control target or the state quantity command, and the measured room temperature during normal operation, and a control parameter determination unit configured to determine the control parameter by using the parameter and a formula derived from the model regarding the heat characteristic of the control target.