To provide a pharmaceutical, in particular a compound which can be used as a therapeutic agent for irritable bowel syndrome (IBS). It was found that a tetrahydroisoquinolin-1-one derivative having an amide group at the 4-position or a pharmaceutically acceptable salt thereof has an excellent bombesin 2 (BB2) receptor antagonistic action. It is also found that the tetrahydroisoquinolin-1-one derivative is highly effective on bowel movement disorders. From the above, the tetrahydroisoquinolin-1-one derivative of the present invention is useful as a therapeutic agent for diseases associated with a BB2 receptor, in particular IBS.