To provide a sheath device for an endoscope which allows an observation window of the endoscope to be preferably washed and also facilitates suction/removal or the like of body fluid accumulated in a large amount in an observed part, and allows a user to economically cope with the breakage of a sheath.

At least a suction nozzle 23 is provided in a connection adapter portion 22, and a sheath portion 21 is configured to be movable in an axial direction wit respect to the connection adapter portion 22. By moving the sheath portion 21 in the axial direction with respect to the connection adapter portion 22 while the connection adapter portion 22 is connected to the operation portion 12 of the endoscope 10, a state in which the distal end surface 21a of the sheath portion 21 is positioned forward from the distal end surface 11a of the insertion tube portion 11 of the endoscope 10, and a state in which the distal end surface of the sheath portion is positioned rearward from the distal end surface portion of the insertion tube portion can be selected.