PURPOSE: To increase the efficiency of circular automatic welding and to make change of position of dividing point free by running a welding head over the whole circumference, detecting an attitude during welding by counting the number of pulses and at the same time, stepping welding conditions, automatically when arrived at a set angle.

CONSTITUTION: Dividing points are welding condition of circular welding are inputted from a setting section 11. The condition is fetched in by a CPU 10 through an interface circuit 12 and stored in an RAM 13. A torch is set at a starting point of welding and rotated once, and the number of counts of a pulse count circuit 19 at this time is fetched in by the CPU 10. The CPU 10 calculates the number of pulses of each angle and stores in the RAM 13. Welding is started and the pulse count circuit 19 is reset. A driving motor 16 is rotated, and pulses are sent from an encoder 18 to a pulse count circuit 15. The CPU 10 compares the number of calculated pulses and the number of sent pulse counts, and when they coincide, steps the welding condition. When returned to a starting point of welding after continuing this operation, shifted to crater processing.