The present invention aims to provide a therapeutic or prophylactic agent forschizophrenia, which therapeutic or prophylactic agent can treat especiallypositivesymptoms of schizophrenia and does not cause impaired information processingrelated to cognitive deficiencies or the like which is a symptom ofschizophrenia.That is, a therapeutic or prophylactic agent for schizophrenia, comprising asaneffective ingredient a compound having a specific morphinan skeletonrepresented bythe compound 1 below or a pharmaceutically acceptable acid addition saltthereof,was provided.