1. An alignment method, comprising: disposing an alignment mark provided to a positioned member and a reference mark provided to a surface of an alignment mask so that the alignment mark and the reference mark can face each other; capturing an image from the other surface side of the alignment mask, which is the opposite surface of the alignment mask from the surface where the reference mark is disposed, the image concurrently showing the alignment mark and the reference mark; performing a surface treatment on at least a region of the positioned member side of the alignment mask, which is captured as the image, rather than on the reference mark side thereof, the surface treatment providing a high contrast ratio to each of the alignment mark and the reference mark on the captured image; and thereafter aligning the alignment mark with the reference mark, while checking the image.