In order to improve the resection efficiency, operability, and safety of endoscopic mucosal resection operations, a method has conventionally been employed wherein a cushion agent such as physiological saline is injected into the layer below the area designated for resection, causing the lesion to lift and protrude (hereafter simply referred to as "protrusion"), after which the lesion is removed. It is difficult to accurately remove the intended area using conventional cushion agents because applying pressure to the protrusion tends to cause deformation thereof, the degree of protrusion is low, and the cushion agent diffuses immediately after injection into the peripheral tissue, thereby causing the protrusion to disappear. The present invention solves these problems by employing a polysaccharide having a pseudoplastic viscosity such as xantham gum, carrageenan, gellan gum, guar gum, locust bean gum, sacran, or the like as a cushion agent.
