This magnetostrictive torque sensor 10 includes a rotating shaft 11 used to rotate according to an input torque and provided with magnetostrictive films 14A and 14B, an excitation coil 12 configured to apply an alternating magnetic field 31 to the magnetostrictive film, and detection coils 13A and 13B each of which detects a change in the magnetic characteristic of an associated one of the magnetostrictive films. The magnetostrictive torque sensor is configured so that a bias magnetic field is added to the alternating magnetic field from a bias power supply 17 so as to satisfy the following conditions: Hm −Hin>−Hn where Hm (>0) is an applied magnetic field corresponding to a maximum magnetic permeability obtained according to a magnetic hysteresis curve 34 of the magnetostrictive film, which shows magnetization caused by the alternating magnetic field, Hn (>0) is an applied magnetic field corresponding to an end of a range in which a discontinuous magnetization is performed, and Hin (>0) is an applied magnetic field that determines a sensitivity range to be set on a magnetostrictive sensitivity curve representing a magnetostrictive sensitivity exhibited by the magnetostrictive film.