An object of the present invention is to provide a drug which prevents progress of Alzheimer's disease and a method of preventing progress of Alzheimer's disease. 1-(3-(2-(1-benzothiophen-5-yl)ethoxy)propyl)azetidin-3-ol or a salt thereof has an effect of suppressing brain atrophy and is useful as an agent for preventing or treating brain atrophy. Brain atrophy observed in aging or neurodegenerative diseases can be prevented or treated by administering 1-(3-(2-(1-Benzothiophen-5-yl)ethoxy)propyl)azetidin-3-ol or a salt thereof.
