An antibody has as a target molecule a ubiquitin protein comprising a phosphorylated serine residue at position 65. In addition, a method is provided for specifically detecting Parkinsons disease at an early stage, in which a target molecule is a ubiquitin protein comprising a phosphorylated serine residue at position 65, a pharmaceutical composition for definitively treating or preventing Parkinsons disease, and a method for screening for the pharmaceutical composition.