To provide a torque sensor capable of improving accuracy and sensitivity and facilitating assemblage.

A first cylindrical member 21 is concentrically fixed to one of input/output shafts 3 and 4 concentrically connected to each other via an elastic member 7 so that they can be relatively rotated, and a second cylindrical member 21 is concentrically fixed to the other. The ring-shaped part 23b of the second cylindrical member 23 is inserted into the ring-shaped part 21b of the first cylindrical member 21. Magnetic flux or light that passes through the ring-shaped parts 21b and 23b of both cylindrical members 21 and 23 radially opposed to each other is generated. On the basis of changes in the amount of magnetic flux or light which passes through the ring-shaped parts 21b and 23b on the basis of changes in the circumferential relative locations of both cylindrical members 21 and 23, a signal processing device outputs a signal corresponding to torque transmitted by the input/output shafts 3 and 4.