PROBLEM TO BE SOLVED: To provide a medical instrument which allows an operator to confirm the projecting state of an outer cylinder and an inner cylinder at hand of the operator.SOLUTION: A medical instrument 1 includes: an outer needle 2； an inner cylinder 3 inserted into the outer needle 2； and a treatment implement 4 inserted into the inner cylinder 3. The outer needle 2 is movable between a first position Pwhere the tip is projected from the forward end of the inner cylinder 3 and a second position Pwhere the tip is retreated from the forward end of the inner cylinder 3. The base end part of the inner cylinder 3 is provided with a projection member 8 projected in the radial direction and a turning member 15 for the outer cylinder, which is supported on the projection member 8 so as to be freely turnable and can come close to and separate from the outer peripheral surface of the outer needle 2. The base end part of the outer needle 2 is provided with an engaging member 5 which can be engaged with the turning member 15 for the outer cylinder. The turning member 15 for the outer cylinder includes: a first engagement part 19 for holding the outer needle 2 in the first position Pby engagement with the engaging member 5； and a second engagement part 20 for holding the outer needle 2 in the second position Pby engagement with the engaging member 5.
