To provide a novel therapeutic agent for nocturnal pollakiuria. A therapeutic agent for nocturnal pollakiuria which contains, as an active ingredient, (6S)-N-[4-({(2S,5R)-5-[(R)-hydroxy(phenyl)methyl]pyrrolidin-2-yl}methyl)phenyl]-4-oxo-4,6,7,8-tetrahydropyrrolo[1,2-a]pyrimidine-6-carboxamide.本發明之目的在於提供一種新穎之夜間頻尿治療劑。本發明之夜間頻尿治療劑含有(6S)-N-[4-({(2S,5R)-5-[(R)-羥基(苯基)甲基]吡咯啶-2-基}甲基)苯基]-4-側氧-4,6,7,8-四氫吡咯并[1,2-a]嘧啶-6-甲醯胺作為有效成分。