A heat exchanger comprising: refrigerant causing disproportionation; a main heat exchange unit including a plurality of first heat transfer pipes arranged side by side; a sub-heat exchange unit including a plurality of second heat transfer pipes arranged side by side; and a relay unit including a plurality of relay passages connecting the plurality of first heat transfer pipes and the plurality of second heat transfer pipes , each of the plurality of relay passages having one inlet connected to a corresponding one of the plurality of second heat transfer pipes , and a plurality of outlets each connected to a corresponding one of the plurality of first heat transfer pipes , each of the plurality of relay passages distributing the refrigerant flowing from the one inlet , without merging streams of the refrigerant together, and causing the refrigerant to flow out of the plurality of outlets , characterized in that the sub-heat exchange unit is located below the main heat exchange unit , and in that the relay unit is configured to cause a smaller pressure loss of the refrigerant passing through the relay unit than a pressure loss of the refrigerant passing through the sub-heat exchange unit , wherein the relay unit is configured to cause a larger pressure loss of the refrigerant passing through the relay unit than a pressure loss of the refrigerant passing through the main heat exchange unit , and wherein each of the plurality of relay passages has a passage cross-sectional area equal to or more than a passage cross-sectional area of the corresponding one of the plurality of second heat transfer pipes connected to the one inlet , and equal to or less than a total of passage cross-sectional areas of the plurality of first heat transfer pipes connected to the plurality of outlets . refrigerant causing disproportionation; a main heat exchange unit including a plurality of first heat transfer pipes arranged side by side; a sub-heat exchange unit including a plurality of second heat transfer pipes arranged side by side; and a relay unit including a plurality of relay passages connecting the plurality of first heat transfer pipes and the plurality of second heat transfer pipes , each of the plurality of relay passages having one inlet connected to a corresponding one of the plurality of second heat transfer pipes , and a plurality of outlets each connected to a corresponding one of the plurality of first heat transfer pipes , each of the plurality of relay passages distributing the refrigerant flowing from the one inlet , without merging streams of the refrigerant together, and causing the refrigerant to flow out of the plurality of outlets , characterized in that the sub-heat exchange unit is located below the main heat exchange unit , and in that the relay unit is configured to cause a smaller pressure loss of the refrigerant passing through the relay unit than a pressure loss of the refrigerant passing through the sub-heat exchange unit , wherein the relay unit is configured to cause a larger pressure loss of the refrigerant passing through the relay unit than a pressure loss of the refrigerant passing through the main heat exchange unit , and wherein each of the plurality of relay passages has a passage cross-sectional area equal to or more than a passage cross-sectional area of the corresponding one of the plurality of second heat transfer pipes connected to the one inlet , and equal to or less than a total of passage cross-sectional areas of the plurality of first heat transfer pipes connected to the plurality of outlets . <EOS>