The medical instrument 10 houses a medical container 1 including a container body 2, a soft plug body 3 that seals a mouth section 21 of the container body 2. The medical instrument 10 includes: a cap 7 including a cap-side female screw portion 73 having a first screw thread 731 and a cap-side male screw portion 74 having a second screw thread 741； an adapter 30 disposed inside the cap 7, movable in a proximal-end direction, and configured to be screw-engaged with the cap-side female screw portion 73； and a proximal-end side structure body 80 configured to be screw-engaged with the cap-side male screw portion 74. A pitch s1 at the cap-side female screw portion 73 is larger than a pitch s2 at the cap-side male screw portion 74.
