The compound represented by the formula (IA) or a pharmaceutically acceptable salt thereof is a sleep disorder, depression, anxiety disorder, panic disorder, schizophrenia, drug dependence based on orexin (OX) receptor antagonism, It is useful for the treatment or prevention of diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, eating disorders, headache, migraine, pain, gastrointestinal diseases, epilepsy, inflammation, immune related diseases, endocrine related diseases, and hypertension.式（ＩＡ）で示される化合物又はその医薬上許容される塩は、オレキシン（ＯＸ）受容体拮抗作用に基づいた、睡眠障害、うつ病、不安障害、パニック障害、統合失調症、薬物依存症、アルツハイマー病、パーキンソン病、ハンチントン舞踏病、摂食障害、頭痛、片頭痛、疼痛、消化器疾患、てんかん、炎症、免疫関連疾患、内分泌関連疾患、高血圧等の疾患の治療又は予防に有用である。
