A force transmitting mechanism includes: a force adjusting portion that is disposed between a joint portion of an instrument and a force generating portion and that receives force from the force generating portion; and a driving member that passes through the joint portion, that connects the end effector and the force adjusting portion, and that transmits the force applied from the force adjusting portions to the end effector, wherein, by means of displacement of the driving member associated with flexing or bending of the joint portion, the force adjusting portion increases the force transmission efficiency so that an amount of increase in the force transmission efficiency increases with an increase in a displacement amount of the driving member.