To realize accurate continuous mixing at an extremely low flow rate by feeding a plurality of fluids to a junction through electroosmosis and producing a substantially uniform mixed liquid at the junction.

When a switch 116 is closed, a fluid containing ions is fed by electroosmosis from a vial 108 to the free end of a capillary 100 and when a switch 118 is thrown in, the liquid is fed from a vial 110 to the free end of capillary 100. When both switches 116, 118 are closed, the liquid is fed simultaneously from both vials 108, 110 and mixed at a junction 102. Since a fluid having different ion concentration flows in general at a fixed voltage, the switches 116, 118 are kept in closed state at the time of continuous mixing and the flow rate may be controlled using series resistors 120, 122. Typical frequency range suitable for mixing is 10-100Hz and the total flow rate can be regulated by regulating the duty cycle of both switches 116, 118.