A positioning method of a spot welding robot, the spot welding robot having a movable electrode tip and an opposition electrode tip opposed to the movable electrode tip. The method sandwiches a work piece to be welded between the pair of electrode tips and includes driving the movable electrode tip towards the opposition electrode tip with a servo motor and stopping the movement upon contact based upon a prescribed current value. The method further includes measuring an open separation of two opposing tips between the movable electrode tip and the opposition electrode tip and moving the opposition electrode tip towards the moveable electrode tip based upon the preset value and the open separation of the two opposing tips.