An electrolytic cell for electrolysis of sea water comprisinga housing having an opening at the bottom and top of the housing for in-flow of sea water and out-flow of electrolyzed sea water, respectively;a plurality of flat plate-like anodes vertically disposed in the housing with the major surface area of the anodes being parallel to the flow of sea water through the cell;a plurality of flat plate-like cathodes vertically disposed in the housing with the major surface area of the cathodes being parallel to the flow of sea water through the cell;an outwardly projecting portion for passing an electric current provided at the lower side edge of each of the anodes;an outwardly projecting portion for passing an electric current provided at the upper side edge of each of the cathodes;an electric current-passing plate secured to the lower portion of the housing and connected to the portions for passing an electric current to each of the anodes; andan electric current-passing plate secured to the upper portion of the housing and connected to the portions for passing an electric current to each of the cathodes; and whereinthe anodes and the cathodes are alternatingly disposed with respect to each other,the side edges of each of the anodes and the side edges of each of the cathodes, except for the portions for passing an electric current of each of the anodes and each of the cathodes, are spaced from the inner wall of the housing,and each of the flat plate-like cathodes and each of the flat plate-like anodes have an external contour such that the external contour of each of the flat plate-like cathodes, except for the portions for passing an electric current to each of the cathodes, is located inwardly of the external contour of each of the flat plate-like anodes.