PURPOSE: To execute automatic welding of a high quality, by controlling a variable factor by a correcting device so that a measured value of welding deformation and a temperature change of an object to be welded becomes a set correct value.

CONSTITUTION: A correct value 1 having prescribed range is set in advance as to a temperature, is given to an automatic welding machine 2 through a comparator 5, and welding is executed. Subsequently, deformation and temperature of a joint of an object to be welded 3 in the course of this welding are detected by a sensor 4, and its measured value is fed back to the comparator 5. In this regard, sensing by the sensor 4 is continued until its welding ends. When the welding work advances, and said measured value is varied and is shifted from the range of the correct value 1, the comparator 5 sends a signal to the welding machine 2 and stops welding. At the same time, a signal is sent to a correcting device 6, too, and a countermeasure for correction is executed. Subsequently, when the measured value is included in the correct range by said countermeasure for correction, the comparator 5 applies a start signal to the the welding machine 2 again, and also sends a stop signal to the device 6.