Disclosed is a therapeutic or prophylactic agent for a functional bowel disorder,which is useful for the treatment or prevention of a functional bowel disorder(particularly, irritable bowel syndrome) and comprises a morphinan derivativehaving a nitrogenated cyclic substituent or a pharmacologically acceptableacid addition salt thereof as an active ingredient. The therapeutic or prophylacticagent comprises a morphinan derivative having a specified structure (e.g.,N-(17-cyclopropylmethyl-4,5α-epoxy-3,14-dihydroxy-morphinan-6β-yl)-3,4,5,6-tetrahydrophthalimidetartarate (compound 10)) or a pharmacologically acceptable acid addition saltthereof as an active ingredient. [Chemical structure] ·tartarate (10)
