The heat exchanger includes a condenser and a refrigerant passage connected to the condenser. The refrigerant passage allows a refrigerant to flow into and flow out of the condenser in opposite directions. As a result, the refrigerant passage can be provided on one side of the condenser with an inlet and an outlet facing the same direction. The connection between the refrigerant passage and the air conditioning system is carried out on one side of the condenser only, improving the operative efficiency.