PURPOSE: To provide an electrophoretic device that is easy to handle and provides good reproducibility by coating the interior wall surface of a capillary with a polymer.

CONSTITUTION: A platinum electrode 14 of a high voltage generator 13 is immersed in a first buffer solution vessel 11, and the other platinum electrode 15 is immersed in a second buffer solution vessel 12. A capillary 16 is immersed in the solution vessel 11 at its front end and in the solution vessel 12 at its rear end. On the cross section of the capillary 16, a polymer coating layer 18 and a cover layer 19 of polyimide are formed, respectively, on the interior and exterior wall surfaces of silica 17. The cover layer 19 is peeled from the side of the capillary 16 facing the solution vessel 12, to form a detecting portion 20. A UV detector 21 consisting of UV and diode array detectors is provided at the detecting portion 20. The polymer coating layer 18 provided on the inner surface of the capillary 16 causes little electroosmotic flow, enabling samples of negative ions to be easily measured and providing good reproducibility.