PURPOSE: To increase the close contact of each intercellular joint section, formed by subjecting the electrode poles of adjacent plate groups to resistance welding through the penetrating hole of each diaphragm of a container, by pressing the outer surfaces of the joint section opposite to the welded surfaces of the electrode poles into circular forms.

CONSTITUTION: When performing intercellular connection of plate groups 3 installed in a container with a diaphragm 2 placed between them, a positive and a negative electrode pole 4 and 4' are brought into close contact with the penetrating hole 6 of the diaphragm 2 at first. Next, after current-carrying electrodes 5 and 5' having circular projections 7 and 7' lower than the pointed ends of the electrodes 5 and 5' in their peripheries are brought into contact with the back surfaces of the electrode poles 4 and 4', a large current is introduced to the electrode poles 4 and 4' while pressing and deforming them by means of the electrodes 5 and 5' to subject the electrode poles 4 and 4' to resistance welding through the penetrating hole 6. In addition, pressure is applied by the projections 7 and 7' before or after the welding to form concave areas 9 on the outer surfaces of the joint section. As a result, it is possible to facilitate the positioning of the electrode poles 4 and 4' and to increase the airtightness and the close contact of the joint section.