To make it possible to clean the lip part of an extrusion machine without stopping the machine, by providing a first scraper on a tip of an arm extended from an end part fixed on a slider which is movable on one of the rails which are apart from a slit and placed in the lengthwise direction of the slit, and a second scraper in the same way on the other side of the slit.

A first scraper 8a is installed so that its tip is located along the side edge of a slit 4 on a first tip part 2a, the tip being on an arm which is extended from an end part fixed on a first slider 7 which runs on a first rail 6a of linear rails located apart from a slit 4 on the first tip part 2a of a nozzle device 1 and placed in the lengthwise direction of the slit 4. A second scraper 8b in installed in the same way on a second tip part 2b. The tips of the first and second scrapers 8a and 8b move by the moving of the first and second sliders 7a and 7b, in the same direction as the lengthwise direction of the slit 4, or toward either end of the slit 4. Cleaning of foreign matters adhering on the circumference of the slit 4 can be performed while continuing sheet production.