Abstract: A torque detection device has a magnetic flux collecting ring, arranged outside an outer periphery of a magnetic circuit forming member which is provided in a rotating body applied with a torque, for collecting a magnetic flux generated by the magnetic circuit forming member; a detector for detecting the torque applied to the rotating body based on a density of the magnetic flux collected by the magnetic flux collecting ring; and a holding ring for holding the magnetic flux collecting ring and the detector and including an attachment part to be attached to a stationary object on an outer periphery on one side in a radial direction. An attachment-preventing convex part for preventing attachment to the stationary object by contacting the stationary object is formed on one end face in an axis line direction of the holding ring.