To provide a laminating method which achieve high accuracy and high quality in a laminating step of an optical sheet and a display panel. Contact areas between the optical sheet and the sheet holding head are read. At this time, an optical element face of the optical sheet is brought into contact with the sheet holding head, light is irradiated to the contact areas therebetween from a no-optical-element face, and positional information of the optical sheet is read based on the distribution of the reflected light thereof.