Agent for preventing and/or treating functional gastrointestinal disorder

A method for preventing and/or treating a functional gastrointestinal disorder, comprising administering, to a subject with the functional gastrointestinal disorder, rifaximin as an effective ingredient. The functional gastroinstestinal disorder includes a functional esophageal disorder, a functional gastroduodenal disorder (e.g., a functional dyspepsia), a functional bowel disorder (e.g., a functional bloating, a functional diarrhea), a functional abdominal pain syndrome, a functional gallbladder and Sphincter of Oddi disorder, a functional anorectal disorder (e.g., a functional fecal incontinence, a functional anorectal pain, a functional defecation disorder), a functional disorder in neonates and toddlers (e.g., an infant functional diarrhea), a functional disorder in children and adolescents (e.g., a childhood functional abdominal pain, a childhood nonretentive fecal incontinence), and other diseases.