A heat exchanger has first and second heat exchange units disposed one above the other. In a case where the heat exchanger functions as a condenser, refrigerant flows through the second heat exchange unit after having flowed through the first heat exchange unit. An intermediate header unit through which the first heat exchange unit and the second heat exchange unit communicate with each other causes at least a portion of refrigerant having flowed through a first heat transfer pipe group on the windward side of the first heat exchange unit to flow to a fourth heat transfer pipe group. Further, the intermediate header unit causes at least a portion of refrigerant having flowed through a second heat transfer pipe group on the leeward side of the first heat exchange unit to flow into a third heat transfer pipe group or the fourth heat transfer pipe group.