An ejector includes a body including an inflow space into which a refrigerant flows, a passage formation member disposed inside the body and having a conical shape, and a nozzle passage having an annular cross section which functions as a nozzle and a diffuser passage having an annular cross section which functions as a pressure increase portion, the nozzle passage and the diffuser passage being disposed between an inner wall surface of the body and a conical lateral surface of the passage formation member. A drive mechanism that displaces the passage formation member in a direction along a center axis is coupled to an upstream actuating bar which extends from the passage formation member toward the inflow space and is slidably supported by the body. Center axes of the passage formation member, the upstream actuating bar and the inflow space are coaxial with each other.