An ejector includes a shaft coupled to a passage formation member defining a refrigerant passage inside a body, and the shaft is slidably supported by a support member fixed to the body. A drive mechanism moves the shaft in an axial direction to change a passage sectional area of the refrigerant passage. The passage formation member is provided with a vibration suppressive member including a first mobile end that applies a load to enlarge the refrigerant passage and a second mobile end that applies a load to narrow the refrigerant passage. Both the first mobile end and the second mobile end are disposed on a same side of a slide region of the support member in the axial direction.