A novel gas separation membrane having excellent gas permeability and gas separation performance, particularly carbon dioxide (CO2) permeability and excellent separation performance of carbon dioxide to methane (CH4) is provided. Moreover, a novel gas separation membrane having excellent heat resistance, chemical resistance and strength etc. is preferably provided.A gas separation membrane comprising a resin comprising a branched polybenzoxazole has excellent gas permeability and gas separation performance, particularly excellent carbon dioxide (CO2) permeability and excellent separation performance of carbon dioxide to methane (CH4). The resin comprising a branched polybenzoxazole preferably has a cross-linked structure. Furthermore, the resin comprising a branched polybenzoxazole is preferably a hybrid with silica.