The present invention provides a novel crystalline form of an arylalkylamine compound. Specifically, due to the excellent stability of a novel crystalline form of 4-(3S-(1R-(1-naphthyl)ethylamine)pyrrolidin-1-yl)phenylacetic acid, it may be used as an active pharmaceutical ingredient of medicine. In addition, the present invention provides a method for producing the arylalkylamine compound having advantage in industrial manufacturing.本發明提供一種芳烷基胺化合物之新穎結晶形。具體而言,由於4-(3S-(1R-(1-萘基)乙基胺基)吡咯啶-1-基)苯乙酸之新穎結晶形具有優異之安定性,故可使用作為醫藥品之原料藥。並且,本發明提供一種有利於芳烷基胺化合物之工業製造的方法。由於本案中之圖式僅為測定值之曲線圖,無法作為本發明之代表圖。故本案無指定代表圖。