To provide a method for managing lots of filmy product which can automatically give a lot number in production of disposal or division in a manufacturing process for winding a filmy product.

A parent roll is produced with a main painting material applied on the raw fabric of a filmy product, then a child roll is produced by longitudinally cutting the web of filmy product which is painted with the main painting material when necessary during production of the parent roll, and a grandchild roll is produced by longitudinally cutting the web of filmy product which is painted with the main painting material when necessary during production of the child or great-grandchild roll. A lot number of 'ABCD', '9999', '99' or '9999' is automatically given to each of the parent roll, the child roll and the grandchild roll such that a first letter group 1 of 'ABCD' indicates a production site, nature and a type of main painting material, a second letter group 2 '9999' indicates a main painting material number, a third letter group 3 of '99' indicates a roll number, and a forth letter group 4 of '9999' indicates a branch number.