PROBLEM TO BE SOLVED: To provide a configuration for causing a coil of an endoscope with a bending length switching mechanism to reliably generate a stable fixing force.SOLUTION: An insertion instrument comprises: an elongated insertion section 4 to be inserted into a subject an operation section 3 interconnected with the base end side of the insertion section in the longitudinal axis direction S at least two wire members 40 inserted through the insertion section and through the inside of the operation section and movable back and forth in the longitudinal direction an operation member 80 provided in the operation section and a wire member fixing mechanism 60 for restricting the back and forth longitudinal-axis-directional movement of the at least two wire members provided within the operation section. The wire member fixing mechanism comprises: two sliding members 64 which reciprocate by operation in the movement direction of the wire members and in a vertical direction a guide member 61 including at least two guide sections 61c each holding its respective wire member between the guide section and the respective sliding member a rotary cam 63a for reciprocating the sliding members provided between the two wire members and a position adjustment section 61a capable of moving a part of the wire member fixing mechanism to a position where the force of the two sliding members and that of the two wire members are balanced.
