The purpose of the present invention is to provide a rotation speed detection device which achieves improved detection accuracy regardless of a compressor and the operating state of the compressor, and enables the prevention of the breakage of a detection unit. A rotation speed detection device for a compressor, wherein a detection unit for detecting full blades and splitter blades that are blades approaching a compressor casing of the compressor in response to a change in the inductance of a magnetic field is provided. The detection unit is provided in an overlap region in which the full blades and the splitter blades that are all blades can be detected and the exposure pressure is in the range of a gauge pressure of one atmosphere or less.