A method for producing a magnetostrictive torque sensor which detects steering torque applied to a steering shaft. A magnetostrictive film is formed on the steering shaft and then subjected to heat treatment, which decreases a weight ratio of hydrogen included in the magnetostrictive film. Thermal desorption gas analysis is performed on at least a portion of the magnetostrictive film undergoing the heat treatment step. A portion of the magnetostrictive film having a thickness of 40 μm or less is heated at a temperature rise rate of 5° C. per minute. A weight ratio of a total amount of hydrogen desorbed from the portion of the magnetostrictive film due to the heat treatment to a weight before the heat treatment is no more than 3 ppm up to 150° C., wherein the weight ratio is no more than 10 ppm up to 300° C., and no more than 15 ppm up to 400° C.