A heat exchanger (7,107,207,307,407) comprising: a heat transfer tube group made up of a plurality of heat transfer tubes each of which has, inside the heat transfer tube, a flow passage through which refrigerant flows, the plurality of heat transfer tubes that are arranged in a lateral direction being arranged in a longitudinal direction so as to form a plurality of rows; a fin provided on the heat transfer tubes and facilitating heat exchange between refrigerant flowing inside the heat transfer tubes and air; and a bridging header (24,124,224,324,424) into which end portions of the heat transfer tubes are inserted and that causes refrigerant to flow between the heat transfer tubes arranged in a lateral direction of the heat transfer tube group, wherein the bridging header (24,124,224,324,424) has: a base (31,131,431) having a flat plate shape and having insertion holes, into which respective ones of end portions of the plurality of heat transfer tubes are inserted; a corrugated sheet (32,132,232,332) being a plate having a shape of a wave in which crest portions and valley portions are continuously formed, characterised by each of the crest portions being provided so as to cover a pair of the insertion holes arranged in a lateral direction, the valley portions being in contact with the base (31,131,431) on both sides of each of the insertion holes in a longitudinal direction of the base (31,131,431), the corrugated sheet (32,132,232,332) forming, between the corrugated sheet (32,132,232,332) and the base (31,131,431), a header flow passage, through which refrigerant flows, for every the heat transfer tubes arranged in a lateral direction of the heat transfer tube group; and further characterised by a covering plate (34,134) covering the corrugated sheet (32,132,232,332) and pressing the corrugated sheet (32,132,232,332) toward the base (31,131,431). a heat transfer tube group made up of a plurality of heat transfer tubes each of which has, inside the heat transfer tube, a flow passage through which refrigerant flows, the plurality of heat transfer tubes that are arranged in a lateral direction being arranged in a longitudinal direction so as to form a plurality of rows; a fin provided on the heat transfer tubes and facilitating heat exchange between refrigerant flowing inside the heat transfer tubes and air; and a bridging header (24,124,224,324,424) into which end portions of the heat transfer tubes are inserted and that causes refrigerant to flow between the heat transfer tubes arranged in a lateral direction of the heat transfer tube group, wherein the bridging header (24,124,224,324,424) has: a base (31,131,431) having a flat plate shape and having insertion holes, into which respective ones of end portions of the plurality of heat transfer tubes are inserted; a corrugated sheet (32,132,232,332) being a plate having a shape of a wave in which crest portions and valley portions are continuously formed, characterised by each of the crest portions being provided so as to cover a pair of the insertion holes arranged in a lateral direction, the valley portions being in contact with the base (31,131,431) on both sides of each of the insertion holes in a longitudinal direction of the base (31,131,431), the corrugated sheet (32,132,232,332) forming, between the corrugated sheet (32,132,232,332) and the base (31,131,431), a header flow passage, through which refrigerant flows, for every the heat transfer tubes arranged in a lateral direction of the heat transfer tube group; and further characterised by a covering plate (34,134) covering the corrugated sheet (32,132,232,332) and pressing the corrugated sheet (32,132,232,332) toward the base (31,131,431). a base (31,131,431) having a flat plate shape and having insertion holes, into which respective ones of end portions of the plurality of heat transfer tubes are inserted; a corrugated sheet (32,132,232,332) being a plate having a shape of a wave in which crest portions and valley portions are continuously formed, characterised by each of the crest portions being provided so as to cover a pair of the insertion holes arranged in a lateral direction, the valley portions being in contact with the base (31,131,431) on both sides of each of the insertion holes in a longitudinal direction of the base (31,131,431), the corrugated sheet (32,132,232,332) forming, between the corrugated sheet (32,132,232,332) and the base (31,131,431), a header flow passage, through which refrigerant flows, for every the heat transfer tubes arranged in a lateral direction of the heat transfer tube group; and further characterised by a covering plate (34,134) covering the corrugated sheet (32,132,232,332) and pressing the corrugated sheet (32,132,232,332) toward the base (31,131,431).