A heat exchanger comprising: a plurality of heat transfer tubes (1,1a,1b,1A) configured to allow refrigerant to pass therethrough, arranged in a first direction and being spaced from each other; a first header (2, 2b) connected to one end of each of the plurality of heat transfer tubes (1,1a,1b,1A); a second header (2, 2a) connected to an other end of each of the plurality of heat transfer tubes (1, 1a, 1b, 1A); and a plurality of reinforcing elements connected to each of the first header (2, 2b) and the second header (2, 2a), each of the plurality of heat transfer tubes (1, 1a, 1b, 1A) and each of the plurality of reinforcing elements being disposed between the first header (2, 2b) and the second header (2, 2a) and being connected by the first header (2, 2b) and the second header (2, 2a) without being connected by a heat transfer promoting component connecting side surfaces of the plurality of heat transfer tubes (1, 1a, 1b, 1A) and a side surface of each of the plurality of heat transfer tubes (1, 1a, 1b, 1A) and a side surface of each of reinforcing elements, wherein each of the plurality of reinforcing elements is higher in section modulus around a neutral axis than each of the plurality of heat transfer tubes in a first cross-section orthogonal to tube axes of the plurality of heat transfer tubes (1, 1a, 1b, 1A), the neutral axis intersecting the first direction, characterised in that each of the plurality of reinforcing elements has an I-shaped cross-section, and a cross-sectional outer shape of each of the ends (31,32) of each of the plurality of reinforcing elements is the same as the cross-sectional outer shape of each of the flat tubes (1, 1a, 1b, 1A). a plurality of heat transfer tubes (1,1a,1b,1A) configured to allow refrigerant to pass therethrough, arranged in a first direction and being spaced from each other; a first header (2, 2b) connected to one end of each of the plurality of heat transfer tubes (1,1a,1b,1A); a second header (2, 2a) connected to an other end of each of the plurality of heat transfer tubes (1, 1a, 1b, 1A); and a plurality of reinforcing elements connected to each of the first header (2, 2b) and the second header (2, 2a), each of the plurality of heat transfer tubes (1, 1a, 1b, 1A) and each of the plurality of reinforcing elements being disposed between the first header (2, 2b) and the second header (2, 2a) and being connected by the first header (2, 2b) and the second header (2, 2a) without being connected by a heat transfer promoting component connecting side surfaces of the plurality of heat transfer tubes (1, 1a, 1b, 1A) and a side surface of each of the plurality of heat transfer tubes (1, 1a, 1b, 1A) and a side surface of each of reinforcing elements, wherein each of the plurality of reinforcing elements is higher in section modulus around a neutral axis than each of the plurality of heat transfer tubes in a first cross-section orthogonal to tube axes of the plurality of heat transfer tubes (1, 1a, 1b, 1A), the neutral axis intersecting the first direction, characterised in that each of the plurality of reinforcing elements has an I-shaped cross-section, and a cross-sectional outer shape of each of the ends (31,32) of each of the plurality of reinforcing elements is the same as the cross-sectional outer shape of each of the flat tubes (1, 1a, 1b, 1A).