PURPOSE: To surely detect only a projection defect without being affected by various kinds of factors of defects.

CONSTITUTION: A sheet-like film 18 is conveyed along rotation of an inspection roller 11 being folded. A scanning light 25 is emitted from a projector 12 so as to be in contact with an inspection section 18a of the film 18 and is inputted to a photodetector 13 after passing through the inspection section 18a. The photodetector 13 sends a photoelectric conversion signal which is proportional to a quantity of the inputted scanning light 25 to a signal processing circuit 17. The signal processing circuit 17 generates a defect-indication signal when a level of the inputted signal is low. An optical glass 15 having parallel surfaces is provided in an optical path of a laser light 20a. An inclination angle of the optical glass 15 is adjusted by a servo device 28, thereby adjusting the height of the scanning light 25.