A centrifugal turbocompressor including an open-type impeller and a casing compresses a gaseous body that condenses into a liquid. The compressor suppresses erosion due to accumulation of a liquid on a casing surface in the compressor. Such accumulation is possible during the starting time of the compressor, if the gaseous body that has come into contact with the casing condenses on the surface of the casing and changes into liquid droplets, centrifugal force may cause the droplets to accumulate on the surface of the casing positioned outside an impeller, and thus to grow into coarser and larger droplets or a liquid film. If the blade tips of the impeller rotating at high speed scrape the droplets or the film upward, erosion of the blade tips is liable to result.