A centrifugal separator which enables extraction of particles as concentrated liquid of a uniform concentration under a low pressure without damaging to the particles and is particularly suitable for extraction of weak cells such as animal cells. The centrifugal separator includes a plurality of particle collecting chambers (104; 104a) partially defined by an inner wall face (121) of a rotor (103) the diameter of which increases substantially continuously and suddenly comparing with the diameter of another adjacent portion of the inner wall face of the rotor. Particles centrifugally separated from liquid in a separating chamber (109) in the rotor are introduced into the particle collecting chambers in which they are accelerated suddenly to form soil suspension having an increased fluidity. The soil suspension is then introduced into horizontally extending deriving pipes (105; 105a; 105b; 105c; 105d; 105e) of a small sectional area and then extracted to the outside by way of an extracting pipe (118).