An antibody provided by the present invention has a low reactivity with amyloid precursor proteins, and has a higher reactivity with amylospheroids than with amyloid ² fibrils or monomeric amyloid ²-proteins. According to the present invention, an antibody is provided that has a higher reactivity with amylospheroids than with amyloid precursor proteins, and has any one or more of the following properties: (i) a higher activity with amylospheroids than with amyloid ² fibrils (ii) a higher reactivity with amylospheroids than with monomeric amyloid ²-proteins and (iii) an activity of inhibiting neuronal cell death induced by amylospheroids.
