In an ejector, formed in a body is a swirling space which lets a high-pressure refrigerant flowing from a refrigerant inlet port swirl and introduces the swirling high-pressure refrigerant into a depressurizing space in which the swirled high-pressure refrigerant is depressurized and expanded. A passage formation member that defines a nozzle passage and a diffuser passage is shaped to have a cross-sectional area increasing with distance from the depressurizing space. Further, a temperature sensing unit of a drive device that displaces the passage formation member is housed in the body, and the temperature sensing unit and a diaphragm have annular shapes to surround at least the axial line of the passage formation member.