PURPOSE: To keep comfortable outlet air temperature by predicting and calculating a reference control signal with which the evaporator outlet temperature is brought to a target value based on the temperature and flow rate at the evaporator inlet, and controlling the controlling signal between the upper and lower specified values of the control signal.

CONSTITUTION: Delivery control means performs proportional calculation and prediction of a reference refrigerant evaporation pressure with which the outlet air temperature of an evaporator 11 is brought to a target value based on the temperature and flow rate of the evaporator inlet air which mainly affect the outlet temperature. A reference control signal is obtained from the reference refrigerant evaporation pressure based on the specified relationship between the refrigerant evaporation pressure and control signal. Adding allowable variance widths, which are capable of maintaining the comfortableness of passengers, to the upper and lower values of the reference control signal, a control signal is calculated within the widths and based on the outlet air temperature and the target value of the outlet air temperature of the evaporator 11 so that the delivery of a compressor 12 is controlled with a delivery variable control device 13 to make the outlet air temperature comfortable.