Provided is a multi-stage compressor which includes: a first-stage compressing unit which includes a first compressing element with an impeller and a second compressing element with an impeller, the first and second compressing elements being connected to each other; and a rear-stage compressing unit which includes at least one rear compressing element with an impeller, wherein the rear-stage compressing unit receives a fluid compressed and output from the first-stage compressing unit.