The present invention provides a fused polycyclic compound of the following formula, analogues thereof and pharmaceutically acceptable salts thereof; and agents for increasing the sugar-transporting capacity, hypoglycemic agents and pharmaceutical compositions containing the above compounds. This fused polycyclic compound has high medicinal properties and few side-effects, and a therapeutic effect on diabetes. wherein R represents an alkoxy group, R' represents an oxazolylpropionyl group or a thiazolylpropionyl group, and R" represent a hydrogen atom.