To provide a centrifugal compressor capable of widely adapting to any environment without being influenced by environmental conditions.

In this compressor provided with: an impeller 15 rotatably journalled in a casing 13, sucking gas from an intake passage, and feeding fluid to a diffuser; and a diaphragm 16 opposingly arranged on the periphery of the impeller 15 and having a back pressure chamber 17 on its back surface, in which the diaphragm 16 is displaced by differential pressure between impeller side pressure and back pressure chamber pressure, a pressure communication hole 18 is provided through which the back pressure chamber 17 and an inlet passage 21 as an intake passage are communicated with each other.