To actively return refrigerator oil separated from a refrigerant in an evaporator without permitting the oil to stay in the evaporator.

A refrigerant piping 13 of a heat exchanger 15 constituting an evaporator 1 is disposed from the upstream side to the downstream side in a serpentine manner directed upward, and a plurality of parallel parts 21 are communicated with each other through a U bent part 23. To a lower part of the U bent part 23 an oil introduction pipe 25 for leading refrigerator oil is connected, and separated refrigerator oil is returned to a compressor. In the U bent part 23, the oil is likely to be separated with gravity and centrifugal force, and hence the function of an oil separator is ensured naturally.