Abstract: In a monitoring device (11) in the wall (3) of a furnace (1), particularly for capturing the image of an incineration process in the furnace (1), having an inner end (I), an outer end (E), at least one housing (13, 17), and an monitoring element (25) arranged inside the housing (13, 17), extending at least between the inner end (I) and the outer end (E), the monitoring device (11) is provided with a scraper unit (31) that keeps the inner end (I) of the monitoring element (25) free from deposits occurring on the wall (3).