A magnetostrictive torque sensor of the present invention is provided with: a magnetostrictive film; a detection coil; a current direction switching device; and an inversion device, wherein: when the current flows in a direction from one side to another side of the detection coil by the current direction switching device, the torque reacted to the shaft is detected based on the input signal of the inversion device; and when the current flows in a inverse direction from another side to one side of the detection coil by the current direction switching device, the torque reacted to the shaft is detected based on the output signal of the inversion device.