Disclosed is a process for producing an aminoadamantane carbamate derivative which is useful as a significant intermediate of an 11²HSD-1 inhibitor. A process for producing an acid addition salt of a compound represented by the Formula (II): or a solvate of the acid addition salt, wherein R 1 and R 2 are each independently hydrogen, substituted or unsubstituted alkyl or the like； R 3 and R 4 are each independently hydrogen, substituted or unsubstituted alkyl or the like； and R 5 and R 6 are each independently hydrogen, halogen, carboxy, nitro, substituted or unsubstituted alkyl or the like； which comprises separating an acid addition salt of a compound represented by the Formula (II) or a solvate of the acid addition salt by adding an acid to a mixture of syn isomer and anti isomer of a compound represented by the Formula (I): wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are as defined above, in the presence of a solvent.
