PURPOSE: To adjust the detecting range of the torque freely, by engaging one side of a movable gear to an input shaft, engaging the other side thereof to an output shaft, and detecting the torque which is transmitted from the input shaft to the output shaft by the displacement of said movable gear.

CONSTITUTION: When a rotary force is applied to the input shaft 2 and a load is applied to the output shaft 3, the shafts transmit the torque, and the movable gear 8 receives the rotary force and thrust in the axial direction by said torque. The closer the spiral shaped teeth at the outside of the movable gear 8 become a flat shape, the weaker the thrust in the axial direction becomes. The thrust in the axial direction is proportional to the torque, and springs 9 and 10 are extended and contracted so that they are balanced with the thrust. Since the amount of the displacement owing to the extension and contraction of the springs 9 and 10 is proportional to the thrust, the torque can be detected by detecting said amount of displacement. The amount of displacement is detected by the variation in the voltage of a sliding resistor 16 caused by the movement of a pin 15 at the tip of a roller 14.