PURPOSE: To prevent the oxidation and blackening of the outside surfaces of the spot weld zone of stainless steel plates by performing welding while supplying cooling water to near the part where electrodes abut, in spot welding of the stainless steel plates by the electrodes.

CONSTITUTION: The welding part A of superposed stainless steel plates is disposed on a stationary electrode 11, and the bottom 28 of the part A is cooled by the ejection of cooling water. The top 29 of the part A is cooled by the cooling water flowing out through the groove of a movable electrode 1. While the cooling water is supplied to the part A in this way, the electrode 1 is lowered onto the part A, and large electric current is flowed from an electric power source to the part A sandwiched by the electrode 11 and the electrode 1, and the part A is spot-welded while it is pressed by the pressing mechanism of the electrode 1. The part A is cooled at the top and bottom 29, 28 by the cooling water, and since the temp. of these surfaces is suppressed and the surfaces are shut off from the atmospheric air by the cooling water, their oxidation is prevented and the blackening of the surfaces is obviated.