Abstract: An accumulator including a liquid accumulating chamber for accumulating refrigerant, a refrigerant inlet port leading the refrigerant, a refrigerant outlet pipe, an oil return opening, a refrigerant flow generating structure and a refrigerant flow mixing structure. The refrigerant outlet pipe includes an upstream open end exposed to an upper part of the liquid accumulating chamber to discharge the refrigerant from the chamber to outside the chamber. The oil return opening is in the refrigerant outlet pipe to return oil contained in the lower part of the liquid accumulating chamber to a compressor of the refrigeration cycle system. The refrigerant flow generating structure provides refrigerant from the refrigerant inlet port with a given flow, the given flow being produced by a drive force possessed by the refrigerant. The refrigerant flow mixing structure provides the given flow with an upward-and-downward movement to mix the refrigerant.