The present invention is directed to providing an antibody having greater reactivity with amylospheroid than with amyloid β fibers, and the like. The aforementioned antibody includes an antibody having activity of inhibiting amylospheroid formation or activity of inhibiting neuronal cell death induced by amylospheroid. The antibody can be used for a therapeutic and/or preventive agent for Alzheimer's disease, or a screening thereof, a method and reagent for detecting individuals with Alzheimer's disease, and the like.