An indoor unit for an air conditioner, comprising: a heat exchanger that allows supercritical refrigerant to radiate heat to air, a casing in which the heat exchanger is mounted, a fan arranged in the casing, wherein the fan is configured to generate an airflow, the heat exchanger comprising: a plurality of plate fins each having a plurality of through-holes on the planar surface, the plate fins being arranged to be substantially parallel to the airflow; and a plurality of heat transfer tubes inserted into the through-holes in the plate fins,wherein four or more rows (61 to 72) of the heat transfer tubes are arranged to be in the direction crossing the airflow, and are formed so as to be in the upstream-to-downstream direction of the airflow, each of the plate fins is divided between at least one pair of the adjacent rows (61, 62); and the heat exchanger is configured such that the refrigerant flows from the heat transfer tubes in the row on the downstream side of the airflow to the heat transfer tubes in the row on the upstream side of the airflow; and characterized in that each heat transfer tube includes a straight tube which extends in one of the height, width and depth directions of the heat exchanger, whichever is the shortest dimension. a heat exchanger that allows supercritical refrigerant to radiate heat to air, a casing in which the heat exchanger is mounted, a fan arranged in the casing, wherein the fan is configured to generate an airflow, the heat exchanger comprising: a plurality of plate fins each having a plurality of through-holes on the planar surface, the plate fins being arranged to be substantially parallel to the airflow; and a plurality of heat transfer tubes inserted into the through-holes in the plate fins,wherein four or more rows (61 to 72) of the heat transfer tubes are arranged to be in the direction crossing the airflow, and are formed so as to be in the upstream-to-downstream direction of the airflow, each of the plate fins is divided between at least one pair of the adjacent rows (61, 62); and the heat exchanger is configured such that the refrigerant flows from the heat transfer tubes in the row on the downstream side of the airflow to the heat transfer tubes in the row on the upstream side of the airflow; and characterized in that a plurality of plate fins each having a plurality of through-holes on the planar surface, the plate fins being arranged to be substantially parallel to the airflow; and a plurality of heat transfer tubes inserted into the through-holes in the plate fins,wherein four or more rows (61 to 72) of the heat transfer tubes are arranged to be in the direction crossing the airflow, and are formed so as to be in the upstream-to-downstream direction of the airflow, each of the plate fins is divided between at least one pair of the adjacent rows (61, 62); and the heat exchanger is configured such that the refrigerant flows from the heat transfer tubes in the row on the downstream side of the airflow to the heat transfer tubes in the row on the upstream side of the airflow; and characterized in that each heat transfer tube includes a straight tube which extends in one of the height, width and depth directions of the heat exchanger, whichever is the shortest dimension.