To provide a method for efficiently producing exo-glycal derivatives promised for a glycosidase inhibitor etc.

The production method for the exo-glycal derivatives from a cyclic ketose derivative whose noncyclic carbon atom neighboring to an anomer carbon atom is an alkenyl group which has a carbon-carbon double bond, in a cyclic ketose derivative whose anomer position is hemiketal-bonded, is provided. Where a nucleophilic agent is subjected to SN1' nucleophilic addition, enabling the exo-glycal derivatives to have various structures through optional use of a variety of the nucleophilic agents.