PROBLEM TO BE SOLVED: To provide a medicament for treatment or prophylaxis of diseases such as sleep disorder, depression, anxiety disorder, panic disorder, schizophrenia, drug dependence, Alzheimers disease, Parkinsons disease, Huntingtons disease, eating disorder, cephalalgia, hemicrania, pain, digestive diseases, epilepsy, inflammation, immune-related diseases, endocrine-related diseases and hypertension, on the basis of the orexin (OX) receptor antagonist activity.SOLUTION: A medicament comprises a heteroaromatic ring methyl cyclic amine derivative having orexin (OX) receptor antagonist activity and represented by the formula (IA) or a pharmaceutically acceptable salt thereof as an active ingredient.
