In 40 mL of ethyl acetate was dissolved 10.0 g of 1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl}-3-azetidinol, and 5.15 g of L-tartaric acid and 40 mL of ethanol were added thereto, after which the resulting mixture was heated at 65° C. to effect dissolution. After the resulting solution was stirred at 50° C. for 20 minutes, 40 mL of ethyl acetate was added dropwise thereto at the same temperature and the resulting mixture was stirred at 20 to 30° C. for 1 hour. The crystals precipitated were collected by filtration to obtain 13.9 g of 1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl}-3-azetidinol L-tartrate as colorless crystals.
