A method produces a magnetostrictive torque sensor which detects a steering torque applied to a steering shaft by electrically detecting distortion of magnetostrictive films provided on a surface of the steering shaft. A plating step forms the magnetostrictive film on the surface of the steering shaft, and a heat treatment step heat treats the magnetostrictive film on the steering shaft. During the heat treatment step, hydrogen in the magnetostrictive film is decreased so that a hydrogen desorbing peak around 120° C. disappears when the magnetostrictive film is heated after the heat treatment step.