A method for manufacturing a rectangular cell is provided in which a rectangular case containing a power generating element is hermetically sealed by laser welding a sealing plate to an open end of the rectangular case. A sealing plate 2 formed into the same shape as the upper open end of a rectangular case 1 is laid on the upper open end, laser beams 3a to 3d are applied in a downward direction from the horizontal to a line of contact 4 comprising sides "a" to "d" including respective corners "e", and the line of contact 4 is scanned with laser beams 3a to 3d thereby sealing the open end of the case with the sealing plate. <IMAGE>
