Abstract: In a so-called membrane electrophoresis apparatus used for separating a liquid sample containing components having biological activity such as various proteins into the components, there is provided an apparatus for simplifying the operation of applying the liquid sample on a supporting membrane and, moreover, for separating with good accuracy the above mentioned components. A supporting medium (3) for separation comprising a water-retentive membrane material and electrically connected to one electrode (5a) of a direct-current electric power source is wetted by a buffer solution (A) containing leading ions. A supporting medium (7c) and a supporting medium (9) similarly comprising water-retentive materials are respectively wetted by a buffer solution (C) containing terminating ions and a buffer solution containing leading ions and having a pH which is different from that for the above mentioned supporting medium for separation.