The present invention pertains to a therapeutic drug or prophylactic drug for diabetic nephropathy, said drug comprising a compound represented by formula (I) or a pharmaceutically acceptable salt thereof as an active ingredient.本發明關於一種糖尿病性腎病之治療藥或預防藥,其係含有式(I)所表示的化合物或其製藥學的所容許的鹽作為有效成分。