PURPOSE: To automate the following multi-layered welding by only inputting the shift width, by storing a linear operation locus of the first layer in a robot, and deriving an operation locus of the second layer and thereafter from the inputted shift width.

CONSTITUTION: A linear operation locus L1 of the first layer is stored in a teaching and regenerating type welding robot containing an operation control means, in accordance with which the operation processing is executed, and in accordance with this result, the robot is controlled. Subsequently, shift width ΔS corresponding to a weld bead of the first layer and thereafter is given as a parameter from the outside. Also, in accordance with a data of the first layer, a direction vector of a welding torch 8 and a direction vector of the locus L1 are derived, and also the outer product of these two vectors T, P is operated, by which a shift direction of the second layer and thereafter is decided. In this way, the second layer bead 7 is formed along a locus L2, and multi-layer welding is automated by only inputting the shift width ΔS.