A two-stage decompression ejector includes a variable throttle mechanism having a first throttle passage for decompressing a fluid and a valve body for changing a throttle passage area of the first throttle passage, a nozzle having therein a second throttle passage for further decompressing the fluid decompressed by the variable throttle mechanism, and a suction portion for drawing a fluid by a suction effect of a high-velocity jet fluid from the nozzle. The formula of 0.07≦Vo×S/vn≦0.7 is satisfied, in which Vo is an intermediate-pressure space volume (mm3) from an outlet of the variable throttle mechanism to an inlet of the second throttle passage, S is a throttle passage sectional area (mm2) of a minimum passage sectional area portion of the second throttle passage, and vn is a flow velocity (mm/s) of the fluid passing through the minimum passage sectional area portion.