PROBLEM TO BE SOLVED: To provide a drug which inhibits the binding of BAFF to the BR3 receptor and excels in autoimmune diseases and acquired immunodeficiency syndrome or the prevention and/or therapeutic effect of a cancer.SOLUTION: The inhibitor of bonding BAFF to the BR3 receptor includes a compound represented by formula (1), a salt thereof or a solvate of them as an active ingredient.COPYRIGHT: (C)2013,JPO&INPIT【課題】BR3受容体に対するBAFFの結合を阻害し、自己免疫性疾患、後天性免疫不全症候群又は癌の予防及び/又は治療効果に優れた薬剤を提供すること。【解決手段】式(1):で表される化合物、若しくはその塩、又はそれらの溶媒和物を有効成分とするBR3受容体に対するBAFFの結合阻害剤。【選択図】なし