A centrifugal separator includes a rotating body driving and sealing structure in which a hermetically sealed space is formed between a rotating body and an outer case by sealing the inside and outside using a noncontact seal during rotation of the rotating body, in an airtight manner. A rotation coupling unit is provided at the upper end of a centrifugal cylinder, and even when the centrifugal cylinder is deformed during use causing an internal fluid to leak through a fitting portion of a bottom member to the centrifugal cylinder, the fluid leaks in the hermetically sealed space so that the driving system or the like is not contaminated.