To perform alignment of a protective tape having a protective layer with high accuracy, provided is an alignment device (5) to be used for applying a protective tape (PT) to a semiconductor wafer (W), including: a tape holding body (30) configured to hold the protective tape (PT) laminated with a protective layer (PL) having an outer diameter smaller than an outer diameter of the protective tape (PT), and one image pickup means (50) for imaging a plurality of parts of an outer peripheral edge portion of the protective layer (PL), wherein the alignment device is configured to determine a center position of the protective layer (PL) based on positional information on each of the plurality of parts of the outer peripheral edge portion of the protective layer (PL) through determination of the positional information on the each of the plurality of parts based on image data acquired by imaging of the image pickup means (50).