PROBLEM TO BE SOLVED: To provide a catheter capable of smoothly moving a sheath in a living body lumen.SOLUTION: An outer tube 150 of the catheter is configured to be fixed to a relay connector 180 and to be rotatable relative to a unit connector 190 such that an operator can perform an operation of rotating a sheath 110 to be inserted into a living body lumen. Even in a state where the catheter 110 is connected to an external device such as a drive unit, the operator can rotate the sheath 110 by a hand operation. This configuration allows the operator to rotatingly move the distal end of the sheath in the living body, in a procedure using a diagnostic catheter.
