A scaling method in an automatic welding machine equipped with a robot control unit for controlling a robot grasping a welding torch. The robot control unit obtains subsequent taught positions on the basis of taught position data indicative of primary welding points (P1, . . . Pn)) of a welding workpiece. The scaling method includes computing the direction of a normal vector (N) of the surface of the workpiece (WK) based on position data (Q1, Q2, Q3) indicative of any three points on the surface of the workpiece (WK), and obtaining, by correction, scaling points corresponding to the primary welding points on the basis of the direction of the normal vector N.