To ensure more efficient heat exchange by eliminating deviation of void rate among a plurality of channels provided for the heating tubes constituting a heat exchanger and making uniform the flow rate of refrigerant for respective channels thereby making uniform the pressure loss of refrigerant flowing through the heating tubes.

Temperature increases as the air flows through a heat exchanger having heating tubes 21. Temperature of refrigerant flowing through a channel 21a is constant at, all times and the temperature difference between the refrigerant and the air is large on time air flow-in side and the state is reversed on the flow-out side. Since the heating tube 21 has a larger quantity of exchanging heat on the air flow-in side, refrigerant begin to be condensed quicker and the liquid phase s strengthened for the refrigerant lowing on the air flow-in side whereas gas phase is strengthened on the air flow-out side. The strong liquid phase and gas phase are fed together into a mixing chamber 22 and mixed and then arranged into substantrally uniform state before being distributed to respective channels 21a. According to the arrangement, difference of void rate between the flow-in side and the flow-out side is decreased thus decreasing pressure loss among respective channels 21a.