A heat exchanger comprising: a pair of headers (13, 14) inside of which refrigerant flows; and plural flat tubes (11a to 11f) that extend in a direction intersecting a longitudinal direction of the headers and are connected to the headers at different height positions, wherein each of the headers has a first member having formed therein a main flow path, which is arranged to extend in the up-and-down direction and through which the refrigerant flows, and refrigerant connection flow paths (231a to 231f), which extend from the main flow path to an end surface in the direction in which the flat tubes are positioned in order to circulate the refrigerant between the main flow path and plural refrigerant flow paths formed in the flat tubes, and a flat tube holding member to which end portions of the flat tubes are adhered and which holds the flat tubes, and intermediate flow paths (133a to 133f) that interconnect the refrigerant connection flow paths and the plural refrigerant flow paths in the flat tubes are formed in the headers and/or the flat tubes, wherein the first member has a first portion, which extends in the vertical direction and has a shape in transverse cross section having a circular arc and in which shape end portions of that circular arc are joined by a straight line; a second portion, which has an elongated flat shape extending in the vertical direction; and recessed portion spaces formed by the first portion and the second portion, wherein the cross section of the first member orthogonal to the longitudinal direction of the first member is Ω-shaped, wherein the flat tube holding member is bent inward in such a way as to cover both width direction end portions of the second portion of the first member, characterized in that the inwardly bent end portions of the flat tube holding member are positioned in the recessed portion spaces, and in that the headers (13,14) are arranged to extend in an up-and-down direction. a pair of headers (13, 14) inside of which refrigerant flows; and plural flat tubes (11a to 11f) that extend in a direction intersecting a longitudinal direction of the headers and are connected to the headers at different height positions, wherein each of the headers has a first member having formed therein a main flow path, which is arranged to extend in the up-and-down direction and through which the refrigerant flows, and refrigerant connection flow paths (231a to 231f), which extend from the main flow path to an end surface in the direction in which the flat tubes are positioned in order to circulate the refrigerant between the main flow path and plural refrigerant flow paths formed in the flat tubes, and a flat tube holding member to which end portions of the flat tubes are adhered and which holds the flat tubes, and a first member having formed therein a main flow path, which is arranged to extend in the up-and-down direction and through which the refrigerant flows, and refrigerant connection flow paths (231a to 231f), which extend from the main flow path to an end surface in the direction in which the flat tubes are positioned in order to circulate the refrigerant between the main flow path and plural refrigerant flow paths formed in the flat tubes, and a flat tube holding member to which end portions of the flat tubes are adhered and which holds the flat tubes, and intermediate flow paths (133a to 133f) that interconnect the refrigerant connection flow paths and the plural refrigerant flow paths in the flat tubes are formed in the headers and/or the flat tubes, wherein the first member has a first portion, which extends in the vertical direction and has a shape in transverse cross section having a circular arc and in which shape end portions of that circular arc are joined by a straight line; a second portion, which has an elongated flat shape extending in the vertical direction; and recessed portion spaces formed by the first portion and the second portion, wherein the cross section of the first member orthogonal to the longitudinal direction of the first member is Ω-shaped, wherein the flat tube holding member is bent inward in such a way as to cover both width direction end portions of the second portion of the first member, characterized in that the inwardly bent end portions of the flat tube holding member are positioned in the recessed portion spaces, and in that the headers (13,14) are arranged to extend in an up-and-down direction.