To clarify histamine receptor H3 protein function in vivo, the present inventors constructed a nonhuman higher animal in which the expression of a histamine receptor H3 gene was artificially inhibited. As a result, the present inventors found that this nonhuman higher animal showed increased body weight, food intake, blood insulin level, or blood leptin level compared with a control. Thus, the present inventors found that abnormalities in the histamine receptor H3 protein relate to diseases characterized by changes in body weight or food intake, and this has made it possible to screen drugs for treatment or prevention of these diseases, and to examine these diseases.