Descriptions are given for the adults of both sexes and immature stages of Arge hasegawae Takeuchi, 1927, based on the holotype and newly acquired material. Rubus crataegifolius Bunge (Rosaceae) is newly recorded as a host plant. The life history is recorded for the first time based on rearing of material collected in Suwon, Gyeonggi-do, Korea. Arge hasegawae is a multivoltine species with gregarious larval habit at least in early instars. A previous record from Japan is a misidentification.