To economically precisely remove foreign substances contained in pulverized bottle segments in order to effectively utilize recycled materials of PET bottles and utilize a large quantity of the materials as raw materials for engineering plastics, and to provide a large amount of pellets at a low cost from which molded products with few foreign substances are obtained in the case the pellets are formed to be injection molded products.

When recycling recovered PET bottles, flaky foreign substance removal is carried out by measuring the lightness of the flake surface by light irradiation for pulverized foreign substances existing in pulverized flakes and selectively removing the foreign substances with low lightness.