The purpose of the present invention is to provide a compound useful as a prophylactic or therapeutic agent for various diseases and symptoms related to orexin receptors, and a medical usage of the same. The present invention provides a morphinan derivative represented by the general formula (I) below or a pharmaceutically acceptable acid addition salt thereof, the morphinan derivative having excellent selectivity for and antagonism against orexin receptors and excellent therapeutic and prophylactic effects on drug dependence, and an orexin receptor antagonist and a therapeutic or prophylactic agent for drug dependence each containing it as an active ingredient.