Novel indole derivatives represented by formula (I) or salts thereof, wherein R1 is aryl-substituted lower alkyl in which the aryl may be substituted by at least one member selected among halogen atoms, aryls, heterocyclic groups, aryl-substituted lower alkyls, aryl-substituted lower alkenyls, lower haloalkyls, (lower cycloalkyl)-substituted lower alkyloxys, (lower cycloalkyloxy)-substituted lower alkyls, aryl-substituted lower alkynyls, aryloxy-substituted lower alkyls, aryl-substituted lower alkyloxys, lower alkylthios, lower alkyloxys, and alkenyls; and R2 is a lower alkyl, lower alkenyl, aryl, or heterocyclic group optionally substituted by halogeno, lower alkyl, lower alkenyl, or aryl. These compounds have a hypoglycemic activity and a PDE5 inhibitory activity and are useful as a drug.