To perform treatment by readily introducing a device causing minimal invasion even where approach from the body surface is difficult, a medical device includes a guide that is inserted into a lumen; a first balloon at a distal end of the guide, connected to a first flow path extending to a proximal end of the guide; a second balloon on the guide, separated from the first balloon on the proximal-end side and connected to a second flow path extending to the proximal end of the guide; a third balloon extending along the guide from a point between the first balloon and the second balloon to the proximal end and having a port for supplying or discharging fluid at the proximal end; and a cleansing flow path having a discharge port between the first balloon and the second balloon and extending to the proximal end of the guide.