A heat exchanger configured to be used in a vehicle air-conditioning refrigeration cycle for cooling and warming a cabin of a vehicle and exchange heat between air outside the cabin of the vehicle and coolant, comprising: a plurality of tubes arranged in parallel to each other; a plurality of corrugate fins provided between the plurality of tubes ; a first header to which one of the ends of each of the plurality of tubes is connected; a second header to which the other one of the ends of each of the plurality of tubes is connected; a first piping joint provided on the first header or the second header ; and a second piping joint provided on the first header or the second header , the first header and the second header are partitioned in the interiors thereof by partitioning devices , respectively, the plurality of tubes constitute a plurality of tube sets (A, B, C, and D) in accordance with intervals of the interiors of the first header and the second header partitioned by the partitioning devices , the coolant flowed in from one of the first piping joint and the second piping joint passes through the plurality of tube sets while exchanging heat with air outside the cabin of the vehicle and flows out from the other one of the first piping joint and the second piping joint , the plurality of tubes are arranged so that one end is oriented upward and the other end is oriented downward with respect to the vertical direction of the vehicle, the first piping joint or the second piping joint configured to flow out the coolant during the cooling operation is provided on the second header , and three or more of the tube sets (A, B, C, and D) are provided, characterized in that the number of tubes in the respective tube sets (A, B, C, and D) is basically the same. a plurality of tubes arranged in parallel to each other; a plurality of corrugate fins provided between the plurality of tubes ; a first header to which one of the ends of each of the plurality of tubes is connected; a second header to which the other one of the ends of each of the plurality of tubes is connected; a first piping joint provided on the first header or the second header ; and a second piping joint provided on the first header or the second header , the first header and the second header are partitioned in the interiors thereof by partitioning devices , respectively, the plurality of tubes constitute a plurality of tube sets (A, B, C, and D) in accordance with intervals of the interiors of the first header and the second header partitioned by the partitioning devices , the coolant flowed in from one of the first piping joint and the second piping joint passes through the plurality of tube sets while exchanging heat with air outside the cabin of the vehicle and flows out from the other one of the first piping joint and the second piping joint , the plurality of tubes are arranged so that one end is oriented upward and the other end is oriented downward with respect to the vertical direction of the vehicle, the first piping joint or the second piping joint configured to flow out the coolant during the cooling operation is provided on the second header , and three or more of the tube sets (A, B, C, and D) are provided, characterized in that the number of tubes in the respective tube sets (A, B, C, and D) is basically the same. <EOS>