An offline programming device in which a path for preventing interference may be automatically inserted such that a welding robot does not interfere with a jig clamping a workpiece to be welded. The models of the robot, the workpiece and the clamp jig are indicated on a display for determining the path for preventing interference. A simulation is carried out to judge that interference with the jig may occur. When it is judged that interference will occur, data of the preventing path suitable for a straight path passing through the jig are read out from a library including registered preventing paths corresponding to shapes of various jigs. The data of the preventing path includes the three-dimensional data of each point of the path as the incremental value in relation to a reference point of the path. Also, the orientation of a welding torch is registered. The corrected welding program may be downloaded to the actual robot so as to correct the uploaded offline program by using a test result in the actual robot.