A mixing portion that is formed in an area from a refrigerant injection port of a nozzle portion to an inlet section of a diffuser portion in an internal space of a body portion of an ejector, that mixes an injection refrigerant injected from the refrigerant injection port and a suction refrigerant suctioned from a refrigerant suction port is provided. A distance from the refrigerant injection port to the inlet section in the mixing portion is determined such that a flow velocity of the refrigerant flowing into the inlet section of the diffuser portion becomes lower than or equal to a two-phase sound velocity. A shock wave that is generated at a time that a mixed refrigerant is shifted from a supersonic velocity state to a subsonic velocity state is generated in the mixing portion.