PURPOSE: To effectively utilize a robot position correction function by a sensor in weaving weld and lap welding.

CONSTITUTION: When weaving weld is effected by means of reference teach lines (P1→..→Pn) serving as a reference truck, sensing/correction operation modes (Q1-Q1-10;..) in which movement is effected as a robot position is corrected based on an output from an sensor means and an assigned shape truck operation mode in which, starting from the terminal points (Q1-10;..) of one robot truck section drawn during execution of a sensing/correction operation mode, a truck ([B] 1-1;..) in a pre-assigned shape is followed are alternately executed. A plurality of kinds of patterns/sizes are prepared regarding an assigned shape and selected according to a program. When same or similar truck repetition type work like lap welding is executed, a correction data re-utilizing mode in which data for correction obtained during execution of the sensing/correction operation mode is utilized again is utilized.