The control system includes a welding robot which moves a welding torch along a work for welding the work. A robot controller controls driving of the welding robot. A laser sensor head detects a shape change in the work during welding by the welding torch, and a personal computer obtains instruction information for the welding robot in accordance with the shape change, based on a result of detection by the laser sensor head. The robot controller moves the welding torch by controlling the driving of the working robot, based on the instruction information obtained by the personal computer.