The object of the present invention is to protect completely a part of an article having penetrating hole(s) from a surface treatment.To attain said object, a masking member (1A), having fitting part(s) (11A) to fit into said hole(s) of said article, the bottom end(s) of said fitting part(s) reaching the end(s) of said hole(s), and flange(s) (13A) being formed around bottom end(s) of said fitting part(s) around the circumference(s) of said hole(s), is provided. When said masking member (1A) is attached to said part by fitting said fitting part(s) of said masking member (1A) into said hole(s), the bottom end(s) of said fitting part(s) of said masking member (1A) reach(s) the opposite side(s) of said hole(s), and flange(s) (3A) around the bottom end(s) of said fitting part(s) of said masking member (1A) cover(s) circumference(s) of said hole(s), to protect the inside(s) of said hole(s) from paint mist circulating around said article, and from reaching the opposite side(s) of said article, when said article is being spray coated with paint.