A cover 20 for covering a circumferential portion of an outer circumferential surface of a rigid endoscope 10 having an observation window portion 14 provided at a tip thereof includes a flexible outer cover member 22 covering the circumferential portion of the circumferential surface of the rigid endoscope 10 and a tubular member 26, provided inside the outer cover member 22, through which a cleaning fluid to be supplied from a base end of the rigid endoscope 10 to the observation window portion 14 of the rigid endoscope 10 flows inside, and the outer cover member 22 is attached to the outer circumference surface of the rigid endoscope 10 by flexing the outer cover member 22.