An air conditioner for a vehicle including a pump that takes in and discharges a heat medium, a heat medium/air heat exchanger which regulates a temperature of ventilation air by conducting sensible-heat exchange between the ventilation air and the heat medium circulated by the pump, a heat transfer device having a passage through which the heat medium flows and conducts heat transfer with the heat medium, a compressor, a heat medium/refrigerant heat exchanger which regulates the temperature of the heat medium, and a controller which regulates a heat transfer amount with the heat medium in the heat transfer device or heat exchange capability of the heat medium/air heat exchanger such that a temperature of the ventilation air regulated by the heat medium/air heat exchanger approaches a target temperature.