An endoscope device (1, 70) includes a treatment instrument (20, 50, 55, 60, 70), the treatment instrument (20, 50, 55, 60, 70) including a treatment instrument body (24), a distal treatment portion (26) provided in a distal direction side to the treatment instrument body (24), and a rotary joint portion (27) which is configured to rotate the distal treatment portion (26) around an axis relative to the treatment instrument body (24), and an inner peripheral surface (17, 73) which is provided in the endoscope (2) or in a tubular member (71) separate from the endoscope (2) and which defines a treatment instrument insertion passage (18) to insert the treatment instrument (20, 50, 55, 60, 70). The endoscope device (1, 70) includes 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 (24) when the treatment instrument body (24) is rotated around the axis relative to the endoscope (2).
