A connecting structure for medical use includes a first connecting portion 1 and a second connecting portion 2. The first connecting portion 1 includes a threadedly engageable portion 22a, a support portion 22b and a sealing portion 14. The second connecting portion 2 includes a threadedly engageable portion 2c and a sealing portion 2b. The threadedly engageable portions are threadedly engageable with each other. The sealing portions are joinable to each other by advancement of a threaded engagement between the threadedly engageable portions. An operating cylinder 30 is mounted on an outer periphery of the support portion 22b. A torque limiting mechanism 40 is disposed between the operating cylinder 30 and the support portion 22b. The sealing portions 14, 2b can be joined by turning the operating cylinder 30 in a threaded engagement advancing direction. When a rotary torque applied to the operating cylinder 30 reaches a predetermined torque as a result of a resistance generated by the joining of the sealing portions, the operating cylinder 30 is turned free from the support portion 22b. By this arrangement, appropriate sealing properties can be secured and the sealing portions can be prevented from breakages.
