PURPOSE: To make it possible to continuously separate a large number of specimens by unmanned operation, by remarkably increasing a magnetic field gradient by separately mounting ferromagnetic bodies to a separation trough comprising a passage small in the thickness thereof as compared with width and length thereof and the passage.

CONSTITUTION: The titled apparatus consists of a separation trough 6 comprising a passage sufficiently small in the thickness (t) thereof as compared with the width and length thereof, a means 11 for flowing a liquid to be separated to be said trough 6, ferromagnetic bodies 9aW9c and means 3a, 3b for imparting high intensity magnetic fields in a direction at right angles to the surface of the trough 6 to which said ferromagnetic bodies are arranged. Each of the aforementioned ferromagnetic bodies 9aW9c is provided to the surface of the aforementioned passage and extended to the width direction of the passage and has a minute width (w) while a large number of the ferromagnetic bodies are arranged so as to be magnetically separated to each other at predetermined intervals T in the longitudinal direction of the passage. By the above mentioned apparatus, a magnetic field gradient becomes large and the use of a magnetic field as an acting field is enabled and a large number of specimens are continuously separated as liquid chromatography by unmanned operation.