PROBLEM TO BE SOLVED: To provide a pharmaceutical for the prophylaxis or treatment of diseases such as schizophrenia, Alzheimer's disease, cognitive dysfunction, dementia, anxiety disorders, depression, AD/HD (attention-deficit/hyperactivity disorder), drug dependence, convulsion, tremor, and sleep disorder.SOLUTION: There is provided a novel imidazolone derivative represented by general formula (I) and having an action of a positive allosteric modulator with respect to metabotropic glutamate receptor subtype 2 (mGlu2 receptor), or a pharmaceutically acceptable salt of the derivative.【課題】統合失調症、アルツハイマー病、認知機能障害、認知症、不安障害、うつ病、ＡＤ／ＨＤ（注意欠如/多動性障害）、薬物依存、痙攣、振戦、睡眠障害等の疾患の予防又は治療用医薬を提供すること。【解決手段】代謝型グルタミン酸受容体サブタイプ２（ｍＧｌｕ２受容体）に対してポジティブアロステリックモジュレーター作用を有する一般式（Ｉ）で表される新規なイミダゾロン誘導体、又はその医薬上許容される塩。【化１】【選択図】なし
