An endoscope aid attachably and detachably attached to a treatment tool insertion channel of an endoscope includes a flexible tubular-member longer than a total length of the treatment tool insertion channel. The tubular-member has a treatment tool insertion pipe line and a suction pipe line. A distal end part of the tubular-member has a sliding contact part that has an outer periphery coming in sliding contact with an inner peripheral surface of an outlet portion of the treatment tool insertion channel maintained in the shape of a straight pipe irrespective of bending of a bending part of the endoscope and is disposed in the outlet portion, and an extending part that extends from the sliding contact part to a distal end side and is disposed to protrude from an outlet of the treatment tool insertion channel. A distal-end-side opening of the suction pipe line is provided in the extending part.
