An object of the present invention is to provide an excellent drug for preventing or treating spinocerebellar ataxia. 1-(3-(2-(1-benzothiophen-5-yl)ethoxy)propyl)azetidin-3-ol or a salt thereof has an effect of suppressing brain atrophy, especially cerebellar atrophy, and is useful as an agent for preventing or treating spinocerebellar ataxia. Cerebellar atrophy observed in spinocerebellar ataxia can be prevented or treated by administering 1-(3-(2-(1-benzothiophen-5-yl)ethoxy)propyl)azetidin-3-ol or a salt thereof.
