To shorten the operation time and to calculate the correction quantity with high accuracy, by calculating the dislocation of a point of a welding wire on the basis of a contact position of the welding wire and a conductive jig, and operating a robot after correcting the dislocation.

In the first process, a command of the detecting operation for correcting the positional deviation, and a command of the application of voltage are memorized in a memory of a robot. In the second process, the correction quantity of the position of a control point is canceled. In the third process, a contact position of a welding wire 7 and a conductive jig 5, is detected. In the fourth process, the data on the contact position is memorized in a robot control unit 2. In the fifth process, the positional deviation quantity is determined by the operation, to memory the same as the correction quantity of the position of the control point. In the sixth process, the robot is operated after the position of the control point is corrected by the correction quantity. The former contact position is unnecessary, the correction quantity is canceled, and the positional deviation can be calculated on the basis of only the contact position detected this time at all times.