The present invention provides a compound useful as a gastrointestinal prokinetic agent or an improving agent for digestive tract function, which shows strong affinities for serotonin 4 receptors. The present invention relates to a compound of formula (1):wherein Ar is a group of formula (Ar-1) or (Ar-2):or a pharmaceutically acceptable salt thereof. The present invention also relates to a pharmaceutical composition comprising a compound of formula (1) or a pharmaceutically acceptable salt thereof.本發明提供一種化合物，其對血清素4受體顯示出強力親和性，可用作消化道蠕動促進藥或消化道功能改善藥。本發明係關於一種化合物或其藥學上所容許之鹽，該化合物以式(1)表示：[式中，Ar係指式(Ar-1)或式(Ar-2)：本發明亦關於一種醫藥組合物，其含有式(1)所表示之化合物或其藥學上所容許之鹽。
