an apparatus for and a method of controlling a drag roller in a printing machine to move a web with no shift of a printing position and enhance the printing quality remarkably , even when the drag roller varies in diameter due to its temperature change . from a given temperature - rotational - speed table , a controlling unit obtains a rotational speed of the drag roller so as to adjust a circumferential speed of the drag roller , which speed corresponds to the current circumferential surface temperature checked by a temperature monitoring unit . then , a rotational speed changing unit changes the rotational speed of the drag roller to a value equivalent to the rotational speed obtained by the controlling unit .