PURPOSE: To form a superior joint weld zone by automatically changing welding conditions to the next welding conditions when a weld time coincides with the operated and set time in automatic full position circumferential welding for piping joints or the like.

CONSTITUTION: A welding head is moved along a guide rail 12 provided around pipings to be welded, and welding is carried out under different welding conditions by dividing the entire circumferential area to 4 areas, No.1WNo.4. First, the outside diameter D of the guide rail 12, then the moving speed V1 of the welding head in the welding area No.1 and an angle θ1 of division are read respectively, and the time required for welding the area No.1 is operated with a microcomputer, and is stored in the storage address of a storage device. Next, the weld time after the start of actual welding is measured with a microcomputer, and when said time coincides with the previous operation time, the welding conditions are changed to the welding conditions of the next area No.2. In this way, the welding is carried out while changing the welding conditions over the entire area successively to No.3 and No.4.