PURPOSE: To uniformize a liquid-supply amount for plural cells and reduce required power of a pump, by forming a loop-shaped liquid passage at the supply side of electrolytic solution in the pump and connecting a liquid-supply pipe of each cell to the liquid passage, to supply each cell with electrolytic solution.

CONSTITUTION: A loop-shaped liquid passage 4 is connected to a liquid-supply port 3 of a pump 6 by which electrolytic solution is supplied from an electrolytic solution jar 4. With liquid-supply pipes 2 of respective cells 1a∼1d connected with the loop-shaped liquid passage 4, each of cells 1a∼1d is supplied with electrolytic solution. With the pressure in the loop-shaped liquid passage made to be equal throughout the loop, pressure loss in the cell becomes nearly identical to that in the liquid-supply pipe for the cell.