A body-wall-contact-type water tank (12) is equipped with: a water-tank body for storing a fluid to be supplied into a body cavity, and positioned so as to contact a body wall (120) a through-hole which conveys the fluid stored in the water-tank body into the body cavity via an incision formed in the body wall (120), and which is formed in the bottom section of the water-tank body and a connecting means for connecting, in a fluid-tight manner, the water-tank body to the body wall (120) and/or to a retractor (110) attached to the incision.
