Azulene derivatives represented by the following general formula (I) and salts thereof are useful as Na+-glucose cotransporter inhibitors in, for example, remedies for diabetes, etc., in particular, insulin-independent diabetes (type 2 diabetes), insulin-dependent diabetes (type 1 diabetes), etc., and remedies for various diabetes-related diseases such as insulin resistant disease and obesity. These compounds are characterized in that an azulene ring is bonded, either directly or via an optionally halogenated lower alkylene, to a benzene ring and the benzene ring is directly bonded to a sugar residue.