An endoscope device (1, 70) comprising: an endoscope; a treatment instrument (20, 50, 55, 60, 75), the treatment instrument (20, 50, 55, 60, 75) including a treatment instrument body extended in a longitudinal direction, and a distal treatment portion provided in a distal direction side to the treatment instrument body; and an inner peripheral surface (17, 73) which is provided in the endoscope or in a tubular member separate from the endoscope and which defines a treatment instrument insertion passage to insert the treatment instrument (20, 50, 55, 60, 75); characterized in that the treatment instrument (20, 50, 55, 60, 75) comprises a rotary joint portion which is provided between the treatment instrument body and the distal treatment portion and which is configured to rotate the distal treatment portion around an axis relative to the treatment instrument body, the endoscope device (1, 70) further comprises a frictional force application portion (41, 51, 61) configured to apply frictional force to a contact portion between a distal direction side part of the inner peripheral surface (17, 73) and an outer peripheral surface in a distal direction side part of the treatment instrument body when the distal treatment portion is rotated around the axis relative to the treatment instrument body in a state that a force is applied to the distal treatment portion, and thereby configured to regulate a rotation of the treatment instrument body relative to the endoscope towards a direction opposite to a rotational direction of the distal treatment portion, wherein the frictional force application portion (41, 51, 61) includes a projection projecting, from the distal direction side part of the inner peripheral surface (17, 73), toward the outer peripheral surface in the distal direction side part of the treatment instrument body such that the tip of the projection is in contact with the outer peripheral surface, and the frictional force application portion (41, 51, 61) includes first projections as the projection which project on the inner peripheral surface (17, 73) toward an inner peripheral side, and second projections which are provided side by side in a state that each of the second projections has a predetermined length in the longitudinal direction, and with which the first projections are in contact, the second projections projecting on the outer peripheral surface of the treatment instrument body toward an outer peripheral side. an endoscope; a treatment instrument (20, 50, 55, 60, 75), the treatment instrument (20, 50, 55, 60, 75) including a treatment instrument body extended in a longitudinal direction, and a distal treatment portion provided in a distal direction side to the treatment instrument body; and an inner peripheral surface (17, 73) which is provided in the endoscope or in a tubular member separate from the endoscope and which defines a treatment instrument insertion passage to insert the treatment instrument (20, 50, 55, 60, 75); characterized in that the treatment instrument (20, 50, 55, 60, 75) comprises a rotary joint portion which is provided between the treatment instrument body and the distal treatment portion and which is configured to rotate the distal treatment portion around an axis relative to the treatment instrument body, the endoscope device (1, 70) further comprises a frictional force application portion (41, 51, 61) configured to apply frictional force to a contact portion between a distal direction side part of the inner peripheral surface (17, 73) and an outer peripheral surface in a distal direction side part of the treatment instrument body when the distal treatment portion is rotated around the axis relative to the treatment instrument body in a state that a force is applied to the distal treatment portion, and thereby configured to regulate a rotation of the treatment instrument body relative to the endoscope towards a direction opposite to a rotational direction of the distal treatment portion, wherein the frictional force application portion (41, 51, 61) includes a projection projecting, from the distal direction side part of the inner peripheral surface (17, 73), toward the outer peripheral surface in the distal direction side part of the treatment instrument body such that the tip of the projection is in contact with the outer peripheral surface, and the frictional force application portion (41, 51, 61) includes first projections as the projection which project on the inner peripheral surface (17, 73) toward an inner peripheral side, and second projections which are provided side by side in a state that each of the second projections has a predetermined length in the longitudinal direction, and with which the first projections are in contact, the second projections projecting on the outer peripheral surface of the treatment instrument body toward an outer peripheral side.