PURPOSE: To control the flow or a fluid by providing electrolytic electrodes which are in contact with an electrolyte and a means which is to form a magnetic field, and reversing directions of the electric field and magnetic field simultaneously and periodically to keep electrodes clean.

CONSTITUTION: Electrodes 2,2' are provided intersecting perpendicularly to the moving direction of a fluid in a pass 1 for circulating the electrolyte solution of a fuel cell, and magnets 3,3' are provided intersecting perpendiculary to the moving direction of the fluid and to the electric field of electrodes 2,2' in the external. The fluid is drived and controlled by actions of the electric field and magnetic field, and directions of electric field and magnetic field are reversed with switches 5 simultaneously and periodically to reverse electrode reactions without changing the control direction of the fluid. Thus deposited metal is dissolved during a next cycle, electrodes are kept clean always, and the reaction can be continued normally.