To provide a mechanism for detecting torque through a simple structure while maintaining a high torque transmission efficiency.

In the mechanism for detecting an input torque to a crankshaft 2 by detecting relative rotational amount between the crankshaft (input shaft) 2 and a resultant force shaft (output shaft) 4 arranged coaxially and rotatably each other through a resilient body, the resilient body comprises a torsion bar 25 and torsion thereof is converted into axial displacement of a cam plate 31 supported slidingly by the crankshaft 2 and axial displacement of the cam plate 31 is converted through a cam mechanism (a cam 33 and a fulcrum pin 34) into rotational displacement of the cam plate 31 and detected by a displacement sensor 35. Since an input torque to the crankshaft 2 is transmitted through the torsion bar 25 to the resultant force shaft 4, torque can be detected through a simple structure while sustaining high torque transmission efficiency.