Provided is an air-conditioning device for a vehicle, including: a cooling device configured to cool air passing through a duct; a heater core, which is arranged in the duct on a downstream side of airflow with respect to the cooling device, and is configured to use an engine coolant as a heat source to heat the air; a water valve provided in a coolant circulation system on an upstream side of the heater core; and a controller configured to control those components, in which the controller is configured to decrease an opening amount of the water valve in a predetermined cooling mode. The control is configured to, when the opening amount of the water valve is decreased, decrease a rotational speed of a compressor of the cooling device, and increase a target evaporator temperature of an evaporator of the cooling device, thereby decreasing cooling performance of the cooling device.