Abstract: In a welding machine used on a continuous processing line of strip steel such as a continuous mill line or continuous annealing line for welding the leading end of the following coil to the trailing end of the preceeding coil to provide a continuous section of the strip steel to the line, there is provided a pair of clamping mechanisms for clamping the coil ends to be joined and at least one of the clamping mechanisms is adapted to be movable in the width direction of the strip so as to provide, in combination with a strip width detecting unit, an automatic edge aligning arrangement. In addition to the automatic edge aligning arrangement, there is provided, at the entry end of the welding machine, a coarse edge aligning apparatus which comprises a clamp for clamping the leading end of the following coil and a detecting mechanism for detecting the center of the width of the leading end of the following coil.