The present invention relates to a method for detecting a defect in a barrel portion of a bottle. The defect in the barrel portion of the bottle includes a thin blister and a longitudinal streak. The defect in the bottle barrel is detected by imaging the bottle barrel with a CCD camera based on light which has passed through a light shield plate having a plurality of oblique slits and the bottle barrel, and processing the image of the bottle barrel generated by the CCD camera to determine whether or not the defect is present.