Disclosed is a process for producing an aminoadamantane carbamate derivative which is useful as a significant intermediate of an 11βHSD-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 R1 and R2 are each independently hydrogen, substituted or unsubstituted alkyl or the like; R3 and R4 are each independently hydrogen, substituted or unsubstituted alkyl or the like; and R5 and R6 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 R1, R2, R3, R4, R5, and R6 are as defined above, in the presence of a solvent.