A C-glycoside derivative represented by the following general formula (I) or its salt which is a compound useful as a Na<+>-glucose co-transportation inhibitor in a remedy for, e.g., diabetes, in particular, insulin-independent diabetes (type 2 diabetes) and insulin-dependent diabetes (type 1 diabetes), as well as a remedy for insulin resistance diseases and various diseases relating to diabetes including obesity. This compound is characterized in that the ring B is bonded to the ring A via -X- and the ring A is bonded directly to a sugar residue.