Provided are an intestinal environment-improving agent containing as an active ingredient a compound represented by formula [I] or a pharmaceutically acceptable salt thereof, and a novel medicine useful in the prevention or treatment of conditions such as hepatic encephalopathy and uremia.本發明係提供一種含有下述式[I]所示之化合物或其製藥學上可容許之鹽作為有效成分的腸內環境改善劑、及有用於肝性腦病、尿毒症等疾病之預防或治療的新穎醫藥;