To provide a novel substance having .alpha.-glucosidase inhibiting activity, derived from natural products and being safe, which substance has not only a blood sugar ameliorating activity being effective in the prevention or treatment of diabetes or obesity but also an activity of reducing postprandial hyper-blood sugar, etc. and to provide food containing the same. [MEANS FOR SOLVING PROBLEMS] A substance having .alpha.-glucosidase inhibiting activity, represented by the formula: