To provide a peritoneal dialyzer capable of greatly reducing the cost of dialysis treatment and contributing to save resources by reducing contamination portions in the dialysis treatment, so that replacement of the entire cassette portion is unnecessary for each dialysis treatment, and to provide a cassette used for the same.

An apparatus body and the cassette part are provided, and the cassette portion has a plurality of tubes composing the peritoneal dialyzer circuit. A sending tube for sending a dialysis liquid to a patient who is a user, a return tube whose flow path is separated from the sending tube for introducing the peritoneal liquid sent from the patient, and a drainage tube connected to a drainage tank are included. The sending tube, the return tube, and the drainage tube are disposed to be separated from each other in the cassette portion while the sending tube, the return tube, and the drainage tube are led out of the cassette part separately.