Torque detection device and electric power steering system

A torque detection device, comprising:

• an elastic member that couples a first shaft to a second shaft such that the first shaft and the second shaft are rotatable relative to each other, and that is twisted as a torsional torque is input into a portion between the first shaft and the second shaft;
• an annular magnet that is coaxially fixed to the first shaft, and in which N-poles and S-poles are alternately formed in a circumferential direction;
• a pair of annular magnetic yokes that are coaxially fixed to the second shaft and that surround the magnet in a noncontact state, each of the magnetic yokes including a plurality of lugs that extend in an axial direction and that are arranged at equal intervals in the circumferential direction, and the magnetic yokes being arranged so as to face each other with a gap in the axial direction such that distal end portions of the lugs of one of the magnetic yokes and distal end portions of the lugs of the other magnetic yoke are arranged alternately in the circumferential direction;
• and
• a magnetic sensor that detects the density of magnetic fluxes generated in the magnetic yokes, wherein
• each of the lugs becomes narrower in width toward the distal end and has a curved profile with rounded corners when viewed from a radial direction of the corresponding magnetic yoke.