A body part of a decompression device has a swirl space for swirling a refrigerant that flows from a refrigerant inlet, and a refrigerant outlet that is positioned on an extension line of a swirl center line of the refrigerant and functions as a throttle. Further, a passage cross-sectional area of the refrigerant inlet is configured to be smaller than a twelve-fold value of a passage cross-sectional size of the refrigerant outlet, such that a swirl speed of the refrigerant in the swirl space is increased so as to enable a decompression boiling of the refrigerant around the swirl center line. In such manner, a gas-liquid mixture phase refrigerant securely flows into the refrigerant outlet, and it restricts a fluctuation of a flow amount of the refrigerant flowing toward a downstream side without complicating a cycle structure.