PROBLEM TO BE SOLVED: To improve responsiveness to control and to make control stability compatible with responsiveness at a high level despite of a load condition. SOLUTION: An air-conditioning device for a vehicle comprises a compressor which, in a refrigerant circuit, has correlation between an input signal from an external part and discharge capacity and varies discharge capacity by an input signal value; an vaporizer situated in a fluid passage, serving as a passage for a medium to be cooled, and providing heat absorbing operation; and a sensor to detect the vaporization temperature of the vaporizer. Further, this air-conditioning device comprises a target value computing means to compute the target value of the vaporizer temperature; and a compressor input signal computing means to compute a compressor input signal value by a computation formula containing a compressor item (A) to effect prediction computation of the compressor input signal value necessary and sufficient for the vaporizer temperature to reach a target value during stabilization of operation and a feedback control computation item (B) to contain a deviation between a target vaporizer temperature and the vaporizer temperature. Based on the compressor input signal, discharge capacity of the compressor is controlled.