Endoscope

An endoscope comprising:

• a distal end opening of a treatment instrument insertion channel provided in an insertion portion inserted into a subject, the opening being made at a side surface of a distal end portion at a distal end side of an insertion direction of the insertion portion;
• a treatment instrument elevator base that is, in the distal end portion, provided at a position facing the distal end opening in the treatment instrument insertion channel and leads a distal end of a treatment instrument protruding from the distal end opening, to a desired position;
• a first wall portion along the insertion direction of the distal end opening;
• and a second wall portion at a proximal end side of the insertion direction of the distal end opening and provided with a groove in which a part of the treatment instrument elevator base is fitted when the treatment instrument elevator base is raised, wherein the groove is formed to the second wall portion at a corner between a proximal end in the insertion direction of the first wall portion and an end portion of the second wall portion which is continuous to the proximal end, and wherein as the treatment instrument elevator base is raised, a guide wire opening is releasably engaged by in a state of being in contact with three parts including the treatment instrument elevator base, the first wall portion, and the second wall portion, with a part of the guide wire protruded from the distal end opening being fallen to the groove.