This disease is thought to proceed to lesions as Imbalance of intestinal bacterial flora with administration of antibiotics-->abnormal proliferation of Clostridium difficile-->production of a large amount of toxin-->development of enteritis. Though lesions are found throughout the colon, remarkable findings are seen in the rectum, and the sigmoid colon. As the most recognized change, few mm to 1cm in size, round--oval well-defined plateau or flattened protuberances occur frequently. Endoscopically the surfaces of protuberances are covered with whity-yellow tone pseudomembrane. If lesions become worse, the area of pseudomembrane spreads, coalesces mutually and becomes irregular geographic. When the patient stops taking the antibiotics causing it, the medical condition improves quickly, and roentgenologically and endoscopically protuberances remit, and the surfaces of the mucous membrane become normal.