Provided is a compound useful for preventing/ therapying nonalcoholic fatty liver disease. It relates to a prophylactic/ therapeutic agent for nonalcoholic fatty liver disease containing (R)-2-[3-[[N-(benzoxazole-2-yl)-N-3-(4-methoxyphenoxy)pro pyl]aminomethyl]phenoxy]butyric acid or its salts, or their solvates as effect ingredient.本發明係提供一種有用於預防、治療非酒精性脂肪性肝疾病之化合物。其係關於一種有效成分為(R)-2-[3-[[N-(苯并□唑-2-基)-N-3-(4-甲氧基苯氧基)丙基]胺基甲基]苯氧基]丁酸、或其鹽、或該等之溶劑合物的非酒精性脂肪性肝疾病之預防及/或治療劑。