The present invention provides a therapeutic agent for overactive bladder comprising, as an active ingredient, a tricyclic compound represented by formula (I): ##STR00001## [wherein R.sup.1 represents a hydrogen atom, substituted or unsubstituted lower alkyl, and the like; X.sup.1--X.sup.2--X.sup.3 represents CR.sup.5.dbd.CR.sup.6--CR.sup.7.dbd.CR.sup.8, CR.sup.5.dbd.CR.sup.6--S, and the like; Y represents --CH.sub.2S--, --SOCH.sub.2--, and the like; and R.sup.2 represents a hydrogen atom, and the like] or a pharmaceutically acceptable salt thereof.