In the present invention, the production of the masking member can be started early, and the mold for the masking member, being highly accurate, can be manufactured in a short period of time, moreover the effects of said thermal, contraction of the molded masking member can be modified precisely and easily in a short period of time, further shortening the production time of said masking member. To obtain such object, the present invention provides a method for manufacturing a masking member (1) made of a thermoplastic resin, including; the preparation of mold using the CAD data relating to the design of the part (2) which is subject to masking, and the preparation of a thermoplastic resin mold with which to form a specific masking member to protect the area. Said masking member (1) is manufactured by vacuum and/or pressure forming a thermoplastic resin sheet, after which it is trimmed by a robot operated using the trimming position data obtained from the CAD data.