It is an object of the present invention to provide a seam welding warpage prevention method and apparatus capable of preventing warpage caused by cooling contraction after welding, in a case where workpieces are different from one another in material and thickness, and thus not uniform in thermal contraction. In the seam welding warpage prevention method for welding a plurality of workpieces W1 and W2 that are not uniform in thermal contraction with respect to an energizing direction, the workpieces W1 and W2 are clamped with a pair of roller electrodes 23 and 33 while applying current. The welding is performed in a state where the roller electrode 33 that abuts on the workpiece W2 having higher thermal contraction is offset in an advancing direction ahead of the roller electrode 23 that abuts on the workpiece W1 having lower thermal contraction.