A heat exchanger exchanging heat between air and refrigerant, the heat exchanger comprising: a plurality of flat tubes that have a flat-shaped outside appearance, that extend in one direction, and that include a plurality of flow paths, which are disposed in a width direction, which extend in the one direction, and through which the refrigerant flows; a plurality of fins that are disposed in an extending direction of the flat tube in a state in which the plurality of flat tubes are accommodated; and a header that is connected to the plurality of flat tubes such that one end portion of each of the plurality of flat tubes is disposed on an inner side, and through which the refrigerant flows in the inner side, wherein the header includes a header body that has a tube shape extending in a vertical direction and that partitions an internal space having a column shape, a partition plate (47,133) that is accommodated in the header body, that extends in a vertical direction, and that divides the internal space into a first space and a second space, where the one end portion of each of the plurality of flat tubes is disposed, in the extending direction, in a state in which the refrigerant is capable of being circulated at an upper end portion and a lower end portion of the internal space, and a nozzle portion (49,62) that is disposed at a lower portion of the first space and that includes a discharge outlet (49A,62A) for blowing out the refrigerant supplied from an outside of the header toward a bottom surface of the header body, and refrigerant circulation portions, which are a part of the first space, are each formed on both sides of the nozzle portion in a width direction, and wherein the bottom surface of the header body includes a first bottom surface for partitioning the first space and a second bottom surface for partitioning the second space, characterized in that the heat exchanger comprises: a first refrigerant guide portion that is provided on the first bottom surface and that includes a first guide surface for guiding the refrigerant in a direction from the first space toward the second space, and in that the first guide surface is a recessed curved surface that is recessed in a direction separated from a lower end portion of the partition plate (47,133). a plurality of flat tubes that have a flat-shaped outside appearance, that extend in one direction, and that include a plurality of flow paths, which are disposed in a width direction, which extend in the one direction, and through which the refrigerant flows; a plurality of fins that are disposed in an extending direction of the flat tube in a state in which the plurality of flat tubes are accommodated; and a header that is connected to the plurality of flat tubes such that one end portion of each of the plurality of flat tubes is disposed on an inner side, and through which the refrigerant flows in the inner side, wherein the header includes a header body that has a tube shape extending in a vertical direction and that partitions an internal space having a column shape, a partition plate (47,133) that is accommodated in the header body, that extends in a vertical direction, and that divides the internal space into a first space and a second space, where the one end portion of each of the plurality of flat tubes is disposed, in the extending direction, in a state in which the refrigerant is capable of being circulated at an upper end portion and a lower end portion of the internal space, and a nozzle portion (49,62) that is disposed at a lower portion of the first space and that includes a discharge outlet (49A,62A) for blowing out the refrigerant supplied from an outside of the header toward a bottom surface of the header body, and a header body that has a tube shape extending in a vertical direction and that partitions an internal space having a column shape, a partition plate (47,133) that is accommodated in the header body, that extends in a vertical direction, and that divides the internal space into a first space and a second space, where the one end portion of each of the plurality of flat tubes is disposed, in the extending direction, in a state in which the refrigerant is capable of being circulated at an upper end portion and a lower end portion of the internal space, and a nozzle portion (49,62) that is disposed at a lower portion of the first space and that includes a discharge outlet (49A,62A) for blowing out the refrigerant supplied from an outside of the header toward a bottom surface of the header body, and refrigerant circulation portions, which are a part of the first space, are each formed on both sides of the nozzle portion in a width direction, and wherein the bottom surface of the header body includes a first bottom surface for partitioning the first space and a second bottom surface for partitioning the second space, a first refrigerant guide portion that is provided on the first bottom surface and that includes a first guide surface for guiding the refrigerant in a direction from the first space toward the second space, and in that the first guide surface is a recessed curved surface that is recessed in a direction separated from a lower end portion of the partition plate (47,133).