An apparatus applies a coating medium onto a coating area of a moving substrate. In the case of direct application, the coating medium is applied onto the outer surface of a material web such as paper or carton, or, in the case of indirect application, the coating medium is applied onto the outer surface of a transfer element such as a transfer roll, which transfers the coating medium onto the material web. The coating mechanism is provided with at least one opening for the discharge of coating medium onto the substrate. A panel element is positioned on at least one side of the two margins of the coating area a certain distance after the opening of the discharge element relative to the direction of discharge of the coating medium in order to prevent any deposits of the coating medium outside of the coating area, which thus defines the respective margins of the coating area.