Abstract: An automatic inspection system detects foreign materials included in a sheet of transparent or translucent resin material such as a polyethylene compound. The automatic inspection system comprises an extruder for extruding a resin material into a sheet, means for withdrawing the extruded sheet along a path of travel, means disposed between the extruder and the withdrawing means for permitting the sheet to having down by gravity into a U-shape, sensor means for detecting a vertical position of the U-shaped portion of the sheet, controller means for adjusting the speed of sheet withdrawal for the withdrawing means in response to the output signal from the sensor means, a source of light disposed on one side of the path of travel of the sheet, an image sensor camera disposed on the other side of the path of travel of the sheet in confronting relation to the source of light for receiving light emitted from the source of light and having passed through the sheet to detect foreign materials included in the sheet.