An air conditioner for a vehicle includes: an air conditioning case, a fan, a motor, a cooling passage, a first rib and a second rib. The air conditioning case has an air passage through which air flows. The cooling passage supplies air to the motor from an opening provided in the air passage. The first rib is provided on an inner wall of the air passage upstream of the opening in a flow direction of air. The second rib is provided on the inner wall of the air passage upstream of the first rib in the flow direction of air. A stagnation space is defined between the first rib and the second rib where the air flowing through the air passage stagnates.