The invention provides a novel block copolymer which can significantly improve the adhesion between a molded product composed of a nonpolar polymer such as polypropylene or polyethylene and a coating material or a molded product composed of a polar polymer, as well as a method for producing the same. Disclosed is a block copolymer comprising at least one poly (aromatic vinyl) block having a weight-average molecular weight of 1,000 to 500,000 and at least one cyclized poly (conjugated diene) block, as well as an oxygen scavenger and a modifier for polymer molding material, which comprise the block copolymer as an active ingredient.