PURPOSE: To obtain an inexpensive apparatus with a simple construction which enables separating operation in a short time, by supporting a cylinder having a magnet inside rotatably in a cylindrical container while a magnet is arranged near the container in such a manner as to rotate centered on a shaft parallel with the axis thereof.

CONSTITUTION: A cylinder 2 having a magnet 6 inside is supported concentrically and rotatably in a cylindrical container 1 and a magnet 7 is arranged near the container 1 to be rotated by a motor 8 centered on a shaft parallel with the axis thereof. Then, when the cylinder 2 rotates, a solid-phase liquid existing in a circular space between the container 1 and the cylinder 2 moves together by a friction force at the part contacting the cylinder 2 while being kept at rest at the part contacting the container 1 which causes a violent agitation, but the axial motion thereof is restricted strictly. At this point, when a small amount of a mobile phase liquid is injected from a sample injector 3, it floats or settles in the solid-phase liquid while spiralling as rotary particle. This achieves a distributive balancing of a solute between the mobile-phase liquid and the solid-phase liquid in a very short space of time.