A morphinan derivative represented by the following general formula (I): (in the formula, R1 represents hydrogen, C1-6 alkyl, cycloalkylalkyl (the cycloalkyl moiety has 3 to 6 carbon atoms, and the alkylene moiety has 1 to 5 carbon atoms), aralkyl (the aryl moiety has 6 to 10 carbon atoms, and the alkylene moiety has 1 to 5 carbon atoms) and the like, R2 represents hydrogen, C1-6 alkyl, C3-6 cycloalkyl, C6-10 aryl, aralkyl (the aryl moiety has 6 to 10 carbon atoms, and the alkylene moiety has 1 to 5 carbon atoms) and the like, R3, R4 and R5 represent hydrogen, hydroxy, carbamoyl, C1-6 alkoxy, C6-10 aryloxy and the like, R6a, R6b, R7, R8, R9, and R10 represent hydrogen and the like, X represents O or CH2, and Y represents C═O, SO2, an atomic bond and the like), or an acid addition salt thereof is used as an analgesic.