To provide a torque detecting device and its manufacturing method where no torque detection value varies depending on the rotational angles of a spindle, no output changes depending on displacement error and the like in the axial direction, and a steering feeling is good even applied to a motorized power steering.

The torque detecting device is provided with an input axis 1 (rotation axis) to which a prescribed residual stress or plastic distortion is applied, a cylindrical multiplex winding coil 11 which detects change in permeability to the rotational torque inputted into the input axis 1 (rotation axis). Based on a detection value of the multiplex winding coil 11, the rotational torque inputted to the input axis 1 (rotation axis) is detected.