This invention provides a method of treating a neurodegenerative disease selected from the group consisting of Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, comprising administering a pharmaceutically effective amount of an agent capable of suppressing expression or activity of SHP-1/-2 (Src homology region 2 domain-containing phosphatase-1/-2) or FcγRIIB (IgG Fc receptor II-B) to a subject having the neurodegenerative disease, wherein the agent capable of suppressing expression of SHP-1/-2 or FcγRIIB is selected from the group consisting of miRNA, siRNA, shRNA, antisense oligonucleotide, and a combination thereof capable of specifically binding to mRNA of SHP-1/-2 or FcγRIIB, and the agent capable of suppressing activity of SHP-1/-2 or FcγRIIB is selected from the group consisting of an antibody, an aptamer, an antagonist, and a combination thereof capable of specifically binding to a protein of SHP-1/-2 or FcγRIIB.