An object of the present invention is to provide a pharmaceutical composition or food or drink composition comprising an active ingredient that suppresses functional expression of Oscar protein. Another object of the present invention is to provide a pharmaceutical composition or food composition for preventing or treating kidney disease. A further object of the present invention is to provide a pharmaceutical composition or food or drink composition that suppresses functional expression of Oscar in a living organism in order to suppress functional expression of FGF23. A still further object of the present invention is to provide a method for evaluating an effect, in the body, of an active ingredient that suppresses functional expression of Oscar protein. The above objects are achieved by at least one member selected from the group consisting of antagonists of the Oscar protein； genome editing systems that target Oscar gene； at least one RNA molecule selected from the group consisting of siRNA, shRNA, and miRNA that target Oscar mRNA, or vectors capable of expressing the RNA molecule； and antibodies that specifically bind to the Oscar protein and suppress function of the Oscar.
