The present invention provides a compound which is useful as an active ingredient of a pharmaceutical composition, in particular, a pharmaceutical composition for preventing or treating diseases or conditions associated with and/or mediated by β-secretase activity, hydrolysis of a β-secretase site of a β-amyloid precursor protein, and/or β-amyloid protein accumulation, including a pharmaceutical composition for preventing or treating diseases including, but not limited to, Glaucoma, MCI (Mild cognitive impairment) or Alzheimer's disease, especially, Alzheimer's disease.