To provide a compressor applied only to an effective compressor impeller but not applied to an ineffective impeller according to a guideline condition on the peripheral velocity of impellers in the compressor for gradually compressing process gas, containing a hydrogen sulfide component, particularly in a turbo-compressor.

Inside a housing 5 of a compressor, impellers 3, 2 with a right side flow direction 7, and impellers 2 with a left side flow direction 8 behind cooling part 6 are arranged on a shaft 1 respectively having cover plates 4. A shift from an H2S area without danger to a dangerous H2S area is performed behind an outlet of the impeller 3 arranged on the left side on the shaft 1 and large in first or second impeller diameter (peripheral velocity) without the elastic limit of material becoming lower than the critical value. Another impeller 2 with the right side flow direction 8 already in the dangerous H2S area is made small in impeller diameter and formed of material with a lowered elastic limit.