PURPOSE: To prevent deformation of materials to be welded at the time of teaching and to accurately teach the welding position by providing a control means to change over the air pressure at the time of teaching and at the time of welding on an air supply path to a gun cylinder of the arm tip of a playback type robot.

CONSTITUTION: When the industrial robot is set on the teaching mode, the air supply pressure supplied to the gun cylinder 2 from the air supply path 4 is changed over to the low pressure by the control means 10. In addition, when the industrial robot is set on the welding mode, the air supply pressure supplied to the gun cylinder 2 from the air supply path 4 is changed over to the high pressure by the control means 10. Accordingly, at the time of teaching, deformation of the materials 7 to be welded can be prevented and the welding position can be taught accurately to the industrial robot.