An evaporator includes an inlet side space of a leeward side upper tank into which a refrigerant flows from a refrigerant inlet port, and an inlet side turn path that is formed of a group of tubes and connected to the inlet side space. A ratio of a total passage cross-sectional area AT1 of the group of tubes forming the inlet side turn path to an inlet passage cross-sectional area Ain of the refrigerant inlet port is set at 3.5 or less, and a ratio of a longitudinal direction length Lg1 of the inlet side space to an inlet equivalent diameter Din of the refrigerant inlet port is set at 25 or less. Further, a Reynolds number Re of the refrigerant that has flowed into the inlet side turn path is set at 1800 or more.