A sheath device for inserting a catheter into a patient's body is described. The device has a first sheath with a proximal end and a distal end. When the device is used as intended, the distal end of the first sheath is provided for arrangement in the patient's body and the proximal end of the first sheath is provided for arrangement outside the patient's body. The first sheath comprises a tubular section and a sheath housing, which is disposed at the proximal end of the section and has a receiving channel for a strand-shaped body. The device solves the problem of reliably fixing a second sheath or a catheter with respect to the first sheath by providing a clamping element on the receiving channel for fixing a strand-shaped body in the receiving channel by way of clamping.