A process for advantageously producing tablets having an improved release property and an excellent stability to change with time is provided. The process is for producing tablets containing a morphinan compound represented by the Formula (I) below or pharmaceutically acceptable acid addition salt thereof and an acidic substance such as fumaric acid, maleic acid or adipic acid, and characterized in that the morphinan compound or a pharmaceutically acceptable acid addition salt thereof is granulated by wet granulation together with (an) excipient(s) prior to adding the acidic substance thereto.
