The invention provides a morphinan derivative of the Formula (I): (wherein R.sup.1 is methyl, cyclopropylmethyl or the like; R.sup.2 and R.sup.3 are hydroxy, methoxy, acetoxy or the like; both Y and Z are valence bonds, --C(.dbd.O)-- or the like; X is C.sub.2-C.sub.5 carbon chain (one of the carbon atoms may be substituted by oxygen, sulfur or nitrogen) constituting a part of the ring structure, or the like; (R.sup.4).sub.k is substituted or non-substituted benzene fused ring, carbonyl group or the like; R.sup.9 is hydrogen or the like; R.sup.10 and R.sup.11 are bound to represent --O--, or the like, and R.sup.6 is hydrogen or the like) or a pharmaceutically acceptable acid addition salt thereof. The invention also provides a therapeutic or prophylactic agent for urinary frequency or urinary incontinence, comprising as an effective ingredient the morphinan derivative or the pharmaceutically acceptable acid addition salt thereof; a method for therapy or prophylaxis of the diseases.