A heat exchanger comprising: a plurality of plate-shaped fins stacked at predetermined fin pitches, each of the plate-shaped fins being provided with a plurality of notches arranged in a longitudinal direction of the plate-shaped fins ; and a plurality of heat transfer tubes having a flattened shape, each of the heat transfer tubes being extended in a stacking direction of the plate-shaped fins and disposed in a corresponding one of the notches , each of the plurality of plate-shaped fins including, at circumferential portions thereof defining the notches , fin collars being in contact with an outer circumference of the heat transfer tube, each of the fin collars including at least one reflare section bent in a direction opposite to the side surface of the heat transfer tube being in contact with the fin collar , the plate-shaped fins being arranged at the predetermined fin pitches so that the reflare section of one of the adjoining plate-shaped fins comes into contact with another one of the adjoining plate-shaped fins , each of the heat transfer tubes having a plurality of flow passages formed inside thereof arranged in a long axis direction of the heat transfer tube, in each of the fin collars provided at the circumferential portions defining the same notch, a plurality of the reflare sections are provided along the long axis direction of corresponding one of the heat transfer tubes , characterized in that the at least one reflare section having a tip portion drawn apart from the adjoining plate-shaped fin, a distance between a first end portion serving as a windward side end portion of the heat transfer tube and the tip portion that is closest to the first end portion being longer than a distance between a second end portion (lb) serving as a leeward side end portion of the heat transfer tube and the tip portion that is closest to the second end portion . a plurality of plate-shaped fins stacked at predetermined fin pitches, each of the plate-shaped fins being provided with a plurality of notches arranged in a longitudinal direction of the plate-shaped fins ; and a plurality of heat transfer tubes having a flattened shape, each of the heat transfer tubes being extended in a stacking direction of the plate-shaped fins and disposed in a corresponding one of the notches , each of the plurality of plate-shaped fins including, at circumferential portions thereof defining the notches , fin collars being in contact with an outer circumference of the heat transfer tube, each of the fin collars including at least one reflare section bent in a direction opposite to the side surface of the heat transfer tube being in contact with the fin collar , the plate-shaped fins being arranged at the predetermined fin pitches so that the reflare section of one of the adjoining plate-shaped fins comes into contact with another one of the adjoining plate-shaped fins , each of the heat transfer tubes having a plurality of flow passages formed inside thereof arranged in a long axis direction of the heat transfer tube, in each of the fin collars provided at the circumferential portions defining the same notch, a plurality of the reflare sections are provided along the long axis direction of corresponding one of the heat transfer tubes , characterized in that the at least one reflare section having a tip portion drawn apart from the adjoining plate-shaped fin, a distance between a first end portion serving as a windward side end portion of the heat transfer tube and the tip portion that is closest to the first end portion being longer than a distance between a second end portion (lb) serving as a leeward side end portion of the heat transfer tube and the tip portion that is closest to the second end portion . <EOS>