In a multistage centrifugal compressor, a plurality of impellers is attached to the same rotary shaft. Vaned Diffusers and vaneless diffusers are used, as diffusers, for respective compressor stages configuring the compressor. The vaned diffusers are continuously used from the first compressor stage to the middle compressor stage, and the vaneless diffusers are used for the last compressor stage and the previous stage. While high efficiency is maintained at the compressor stages having the vaned diffusers, an operating flow range is secured at the compressor stages having the vaneless diffusers.