The invention provides a morphinan derivative of the Formula (I): Äwherein R<1> is methyl, cyclopropylmethyl or the like; R<2> and R<3> are hydroxy, methoxy, acetoxy or the like; both Y and Z are valence bonds, -C(=O)- or the like; X is C2-C5 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<4>)k is substituted or non-substituted benzene fused ring, carbonyl group or the like; R<9> is hydrogen or the like; R<10> and R<11> are bound to represent -O-, or the like, and R<6> is hydrogen or the likeÜ 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, and use for the diseases. The compounds of the invention are useful as a new therapeutic or prophylactic agent for urinary frequency or urinary incontinence, free from side effects, and useful for the method for therapy or prophylaxis of the diseases and for use for the diseases.