A heat exchanger, comprising: a plurality of refrigerant flow paths each being a flow path into which refrigerant flows in a gas state and out of which the refrigerant flows in a liquid state, the plurality of refrigerant flow paths including upstream-side flow paths allowing passage of the refrigerant in the gas state and a two-phase gas-liquid state, and at least one downstream-side flow path allowing passage of the refrigerant in the two-phase gas-liquid state and the liquid state; an upstream-side heat exchanger including the upstream-side flow paths; a downstream-side heat exchanger arranged below the upstream-side heat exchanger and, including the at least one downstream-side flow path; and at least one merger (51 to 53) for merging the refrigerant flowing out of each of the upstream-side flow paths and causing the merged refrigerant to flow into the at least one downstream-side flow path, the upstream-side heat exchanger and the downstream-side heat exchanger being configured separately, the number of the downstream-side flow paths being smaller than the number of the upstream-side flow paths, the upstream-side heat exchanger and the downstream-side heat exchanger each including heat exchange units, the heat exchange units each including a plurality of radiator fins arranged in parallel with each other at intervals and allowing passage of air through the intervals, and a plurality of heat transfer tubes penetrating through the plurality of radiator fins in an arrangement direction of the plurality of radiator fins, the upstream-side heat exchanger and the downstream-side heat exchanger each having the heat exchange units arranged in an air passage direction, the number of the heat exchange units in the downstream-side heat exchanger being smaller than the number of the heat exchange units in the upstream-side heat exchanger, a total width of the heat exchange units in the air passage direction in the upstream-side heat exchanger and a total width of the heat exchange units in the air passage direction in the downstream-side heat exchanger being the same with each other. a plurality of refrigerant flow paths each being a flow path into which refrigerant flows in a gas state and out of which the refrigerant flows in a liquid state, the plurality of refrigerant flow paths including upstream-side flow paths allowing passage of the refrigerant in the gas state and a two-phase gas-liquid state, and at least one downstream-side flow path allowing passage of the refrigerant in the two-phase gas-liquid state and the liquid state; an upstream-side heat exchanger including the upstream-side flow paths; a downstream-side heat exchanger arranged below the upstream-side heat exchanger and, including the at least one downstream-side flow path; and at least one merger (51 to 53) for merging the refrigerant flowing out of each of the upstream-side flow paths and causing the merged refrigerant to flow into the at least one downstream-side flow path, the upstream-side heat exchanger and the downstream-side heat exchanger being configured separately, the number of the downstream-side flow paths being smaller than the number of the upstream-side flow paths, the upstream-side heat exchanger and the downstream-side heat exchanger each including heat exchange units, the heat exchange units each including a plurality of radiator fins arranged in parallel with each other at intervals and allowing passage of air through the intervals, and a plurality of heat transfer tubes penetrating through the plurality of radiator fins in an arrangement direction of the plurality of radiator fins, a plurality of radiator fins arranged in parallel with each other at intervals and allowing passage of air through the intervals, and a plurality of heat transfer tubes penetrating through the plurality of radiator fins in an arrangement direction of the plurality of radiator fins, the upstream-side heat exchanger and the downstream-side heat exchanger each having the heat exchange units arranged in an air passage direction, the number of the heat exchange units in the downstream-side heat exchanger being smaller than the number of the heat exchange units in the upstream-side heat exchanger, a total width of the heat exchange units in the air passage direction in the upstream-side heat exchanger and a total width of the heat exchange units in the air passage direction in the downstream-side heat exchanger being the same with each other.