Abstract: The present invention is to provide an apparatus for coating an advancing web on a backup roller Using a coating roller, which enables one to measure and control a coating gap between a lip surface of a coating die and the coating roller. The apparatus includes an extended portion which extends outward from each end of a slit portion of the coating die and has a reference surface parallel to the lip surface, the coating die is slidably located on a frame, a distance sensing means is fixed on each side of the coating roller, a distance is measured from the distance sensing means to the surface of the extended portion and the coating gap is controlled by sliding the coating die in a radial direction of the coating roller. Coating material is thereby controllably transferred from the coating roller to the web.