An ejector includes a nozzle, a swirl flow generation portion, a body including a refrigerant suction port and a diffuser portion, a passage forming member, and an actuation device moving the passage forming member. A nozzle passage is defined between the nozzle and the passage forming member. A smallest passage cross-sectional area portion is provided in the nozzle passage. A swirl space that has a shape of a revolution and is coaxial with the nozzle, and a refrigerant inflow passage through which the refrigerant flows into the swirl space are defined in the swirl flow generation portion. The ejector further includes an area adjustment device that changes the passage cross-sectional area of the refrigerant inflow passage. According to this, an efficiency of energy conversion in the nozzle passage can be improved.