Abstract: There is disclosed a control apparatus and a control method in a welding apparatus for enabling a welding torch to trace a weld line with use of an oscillating process. In the control apparatus and control method, the welding torch is oscillated in the left and right directions crossing the weld line with an overpass, and an electric signal is detected responsive to changes in an arc length and a wire extension. The moving average value of the electric signal is calculated for a predetermined smoothing time interval so as to eliminate a high frequency noise component of the electric signal, and there is outputted a low-pass-filtered electric signal having a level of the calculated moving average value. Thereafter, a controller moves the center of the oscillation so as to enable the welding torch to trace the weld line responsive to the filtered electric signal.