To provide a medical instrument in which the amount of sag of an operation wire can be adjusted in a state where a stress is applied as least as possible to the operation wire.

A medical instrument (catheter 10) includes: a long flexible body unit (sheath 16); an operation wire 40 embedded in the body unit and having a distal end disposed on the distal end of the body unit; and a handy operation unit 70 disposed on the base end of the body unit. The base end of the operation wire 40 is coupled to the handy operation unit 70. The medical instrument further includes: a bending operation unit 730 disposed on the handy operation unit 70; and a sag amount adjusting operation unit 770 disposed on the handy operation unit 70. The bending operation unit 730 is used to perform an operation for bending the body unit by pulling the operation wire 40. The sag amount adjusting operation unit 770 is used to perform an operation for adjusting the dispensable amount of the operation wire 40 from the handy operation unit 70 without causing a change in the amount of pull of the operation wire 40 by the bending operation unit 730.