[Problem]To provide a compound useful as a MT1 and/or MT2 receptor agonist.[Solution]The present inventors have studied on MT1 and/or MT2 receptor agonists, and have confirmed that indole compounds have the activity. As a result, the present invention is accomplished. That is, a compound represented by formula (I) or a salt thereof according to the present invention has a MT1 and/or MT2 receptor agonistic activity and has a low ability of migrating into central nervous system. Therefore, the compound or a salt thereof can be used as a peripheral MT1 and/or MT2 receptor agonist, and therefore can be used as a therapeutic and/or prophylactic agent for urinary incontinence, particularly stress urinary incontinence and mixed urinary incontinence.