Abstract: A device that prevents soot in a stud welding machine. In particular, the device includes a cap holder that is fitted on a stud chuck of a stud gun for a stud welding machine and has extenders at the sides thereof. In addition, fixing rods attach the cap holder to the stud gun by connecting the extenders of the cap holder with the sides of the stud gun and a cap that is inserted in the cap holder from below is movably combined with the cap holder by a cap nut, and has an end that comes in contact with an edge of a welding portion of a base material during stud welding. Further, a shock-absorbing member is disposed between the cap and the cap holder, inside the cap holder, and provides an elastic force to the cap.