To provide a torque sensor capable of surely preventing a connection pin for connecting a rotary shaft and a torsion bar from being detached from a communication hole while suppressing cost increase.

One end of a torsion bar 4 is inserted to a shaft through-hole 2a penetrated at a shaft center of a first rotary shaft 2, communication holes 2b and 4a extending in a radial direction are formed at the first rotary shaft and one end of the torsion bar, and a connection pin 6 is mounted on the communication holes. An extension cylinder part of a cylindrical member 11 extended so as to surround the communication hole 2b of the first rotary shaft is provided with a retaining part 17 for preventing the connection pin 6 from being detached from the communication hole 2b.