A sheath assembly 6 includes at least three flexible, tubular members 6a, 6b and 6c through which linear members can be inserted, a first holder 61 configured to hold one end side of the tubular members 6a, 6b and 6c, and a second holder 62 configured to hold the other end side of the tubular members 6a, 6b and 6c, wherein the first holder 61 and the second holder 62 hold the at least three tubular members 6a, 6b and 6c such that sections of the tubular members 6a, 6b and 6c orthogonal to an axial direction thereof are linearly aligned.