To obtain a torque detecting device capable of improving accuracy in detecting torque, reducing the effects of temperature and disturbance magnetic fields affecting detection results, and further being externally installed easily.

The torque detecting device is constituted of a cylindrical shaft 1, a magnetic impedance element 2 arranged along the radial direction of the shaft 1 at a distance from the peripheral surface of the shaft 1 to generate a voltage (e) corresponding to an external magnetic field H0, a bias magnetic field coil 4, a D.C. power source 5, and an A.C. power source 6. The toque detecting device comprises an element driving circuit 3 to drive the magnetic impedance element 2 and an arithmetic circuit 9 to obtain torque acting on the shaft 1 on the basis of the voltage (e) amplified by an amplifier 8.