A torsion bar of a torque detection device converts torque applied between an input shaft and an output shaft to a torsional displacement. A pair of yokes is secured to the output shaft, and forms a magnetic circuit in a magnetic field of a multipolar magnet secured to the input shaft. A magnetic flux guide member has a main body facing the yoke to guide magnetic flux of the magnetic circuit. A magnetic sensor is placed at an extension, and detects magnetic flux guided by the magnetic flux guide member. The magnetic flux guide member is configured to allow magnetic permeance per unit area between the magnetic flux guide member and the yoke to be greater at a location in the main body from which the extension is branched, than at a circumferential end portion of the main body.