Coupler

The invention provides a coupler capable of realizing stress reduction of a connecting component of the coupler when torque is transmitted. The coupler comprises two fixing bodies (20,20) which are fixed on two rotating shafts (84a,85) respectively, and the connecting component (30) inserted into the above fixing bodies. Each fixing body comprises a main body part (21) for inserting the rotating shaft and protruding parts (22) of convex strips which are formed on the periphery of the main body part and arranged at equal intervals. Each protruding part is provided with an extending part (23) formed on the whole length of the main body part and protrudes from one end of the main body part. For each fixing body, the protruding parts thereof are arranged alternatively along a circumference direction and the main body parts are connected in a status of being inserted into the inner side of the extending part of the other fixing body. The connecting component is provided with a plurality of inserting parts arranged