The force transmission mechanism (2) for a medical device according to the present invention is an elongated insertion inserted into the body for the purpose of smoothly rotating a rotating portion that is arranged at the distal end of the inserting portion and rotates around the longitudinal axis of the inserting portion. The force along the longitudinal direction of the insertion portion (3) input on the proximal end side of the portion (3) is supported at the distal end of the insertion portion (3) so as to be rotatable about the longitudinal axis of the insertion portion (3). A force transmission mechanism (2) for a medical device that transmits to the distal end rotating portion (5), the first force transmitting portion that passes through the insertion portion (3) and transmits to the vicinity of the distal end of the insertion portion (3) ( 6), a force conversion unit (7) that is arranged near the tip of the insertion unit (3) and converts the force transmitted by the first force transmission unit (6) into a rotational force, and a force conversion unit (7) Second force transmission unit (8a, 8b) for transmitting the converted rotational force to the tip rotation unit (5) with different rotation speeds Equipped with a.挿入部の先端に配置され、挿入部の長手軸回りに回転する回転部をスムーズに回転させることを目的として、本発明に係る医療機器用力伝達機構（２）は、体内に挿入される細長い挿入部（３）の基端側において入力された該挿入部（３）の長手方向に沿う力を、挿入部（３）の先端に、挿入部（３）の長手軸回りに回転可能に支持された先端回転部（５）に伝達する医療機器用力伝達機構（２）であって、挿入部（３）内を通過して挿入部（３）の先端近傍まで伝達する第１の力伝達部（６）と、挿入部（３）の先端近傍に配置され第１の力伝達部（６）により伝達された力を回転力に変換する力変換部（７）と、力変換部（７）により変換された回転力を、回転数を異ならせて先端回転部（５）に伝達する第２の力伝達部（８ａ，８ｂ）とを備える。
