A therapeutic or prophylactic agent for functional bowel disorders comprising as an effective ingredient a morphinan derivative having a nitrogen-containing cyclic group or a pharmaceutically acceptable acid addition salt thereof is disclosed. The therapeutic or prophylactic agent for functional bowel disorders comprises as an effective ingredient a morphinan derivative or a pharmaceutically acceptable acid addition salt thereof, having a specific structure, such as N -(17-cyclopeopylmethyl-4,5±-epoxy-3,14-dihydroxy-morphinan-6²-yl)-3,4,5,6-tetrahydrophthalimide tartaric acid salt (Compound 10).
