To accurately align a mask with a substrate by supporting the substrate so as not contact with the mask without applying a tension to it, and by precisely detecting a position of a mark for detecting the positions of the substrate and the mask.

The method for aligning the mask with the substrate comprises the steps of: holding a metal mask 12 having a pattern formed therein on a mask mount 4; illuminating the mark 14 for detecting the position placed in a corner of the mask by using a light source 8 and a reflector plate assembly from a lower side, and taking a photograph of the mark 14 with a charge-coupled device camera 10 from above; supporting both sides of a transparent substrate 11 which has been transported to the upper part of the mask 12 while directing the surface to be vapor-deposited downward, with a hook member so as to create a gap between the substrate and the mask; illuminating the mark 13 placed in the corner of the substrate with a light source 9 from above, and taking a photograph of the mark 13 with the CCD camera 10; computing a relative position of the substrate to the mask from the information on the mark position obtained by processing for an image provided by the photographs of the marks of the mask and the substrate, with an arithmetic unit 20; and moving the substrate so that the relative position of the substrate and the mask can be in a predetermined allowable range, on the basis of the computed relative position.