The problem to be solved is to provide an important intermediate for production of an FXa inhibitor. The solution thereto is a method for industrially producing a compound (1) or a compound (4), comprising: [Step 1]: adding a quaternary ammonium salt and a metal azide salt to water to prepare an aqueous solution of an azidification reagent complex comprising quaternary ammonium salt-metal azide salt, and subsequently dehydrating the aqueous solution using an aromatic hydrocarbon solvent to form a mixed solution of the azidification reagent complex comprising quaternary ammonium salt-metal azide salt and the aromatic hydrocarbon solvent with a water content of 0.2% or less; and [Step 2]: adding, to the mixed solution prepared in [Step 1], a compound (2) wherein L represents a leaving group.