A process for producing tablets containing a morphinan compound represented by the Formula or a pharmaceutically acceptable acid addition salt thereof and an acidic substance, which process is 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, and in that the acidic substance is one or more substances selected from the group consisting of fumaric acid, maleic acid, adipic acid and salts thereof. [wherein R 1 is hydrogen, C 1 -C 5 alkyl, C 4 -C 7 cycloalkylalkyl, C 6 -C 8 cycloalkenylalkyl, C 6 -C 12 aryl, C 7 -C 13 aralkyl, C 3 -C 7 alkenyl, furanylalkyl (wherein the number of carbon atoms in the alkyl moiety is 1 to 5), thienylalkyl (wherein the number of carbon atoms in the alkyl moiety is 1 to 5) or pyridylalkyl (wherein the number of carbon atoms in the alkyl moiety is 1 to 5); R 2 and R 3 independently are hydrogen, hydroxy, C 1 -C 5 alkoxy, C 3 -C 7 alkenyloxy, C 7 -C 13 aralkyloxy or C 1 -C 5 alkanoyloxy; Y and Z independently represent valence bond or -C(=O)-; -X-represents a C 2 -C 7 carbon chain (one or more of the carbon atoms therein optionally is(are) replaced by nitrogen, oxygen or sulfur atom(s), and the carbon chain optionally contains an unsaturated bond) constituting a part of the ring structure; k is an integer of 0 to 8; R 4 is(are) (a) substituent(s) in the number of k on the nitrogen-containing ring, which independently represent(s) fluorine, chlorine, bromine, iodine, nitro, hydroxy, C 1 -C 5 alkyl, C 7 -C 13 cycloalkylalkyl, C 6 -C 12 aryl, C 7 -C 13 aralkyl, C 7 -C 13 aralkyloxy, C 1 -C 5 alkoxy, trifluoromethyl, trifluoromethoxy, cyano, isothiocyanato, SR 6, SOR 6, SO 2 R 6, (CH 2) p OR 6, (CH 2) p COR 6, (CH 2) p CO 2 R 6, SO 2 NR 7 R 8, CONR 7 R 8, (CH 2) p NR 7 R 8 or (CH 2) p N(R 7)COR 8, or among the R 4 s in the number of k, two R 4 s bound to the same carbon atom or to the same sulfur atom together represent one oxygen atom to form carbonyl or sulfoxide, or two R 4 s bound to the same carbon atom together represent one sulfur atom to form thiocarbonyl, or four R 4 s bound to the same sulfur atom together represent two oxygen atoms to form sulfone, or among the R 4 s in the number of k, two R 4 s bound to adjacent carbon atoms, respectively, together form benzene fused ring, pyridine fused ring, naphthalene fused ring, cyclopropane fused ring, cyclobutane fused ring, cyclopentane fused ring, cyclopentene fused ring, cyclohexane fused ring, cyclohexene fused ring, cycloheptane fused ring or cycloheptene fused ring, each of said fused rings is non-substituted or substituted by 1 or more R 5 s, wherein R 5 (s) independently represent(s) fluorine, chlorine, bromine, iodine, nitro, hydroxy, C 1 -C 5 alkyl, C 1 -C 5 alkoxy, trifluoromethyl, trifluoromethoxy, cyano, C 6 -C 12 aryl, isothiocyanato, SR 6, SOR 6, SO 2 R 6, (CH 2) p OR 6, (CH 2) p COR 6, (CH 2) p CO 2 R 6, SO 2 NR 7 R 8, CONR 7 R 8, (CH 2) p NR 7 R 8 or (CH 2) p N(R 7)COR 8; R 9 is hydrogen, C 1 -C 5 alkyl, C 1 -C 5 alkenyl, C 7 -C 13 aralkyl, C 1 -C 3 hydroxyalkyl, (CH 2) p OR 6 or (CH 2) p CO 2 R 6; R 10 and R 11 are bound to form -O-, -S- or -CH 2 -, or R 10 is hydrogen and R 11 is hydrogen, hydroxy, C 1 -C 5 alkoxy or C 1 -C 5 alkanoyloxy; p is an integer of 0 to 5; R 6 is hydrogen, C 1 -C 5 alkyl, C 3 -C 7 alkenyl, C 6 -C 12 aryl or C 7 -C 13 aralkyl; and R 7 and R 8 independently are hydrogen, C 1 -C 5 alkyl or C 7 -C 13 aralkyl]