A method for detecting a foreign particle trapped between substrates of a liquid crystal display panel, by which a potential short caused by the particle can be made into a short with reliability, and thus it is possible to make a display defect manifest itself that is caused by the particle. The method is for detecting the presence of a foreign particle trapped between flexible substrates (21, 26) of a liquid crystal display panel (20), between the substrates liquid crystals filled, and the method includes making the panel pass between supporting rollers (3) arranged to support one surface of the panel, and a pressing roller (4) disposed at a position opposed to a space between the supporting units and arranged to press the other surface of the panel, bending the panel, and displacing the substrates with respect to each other in their surface directions.