The present invention relates to a torque-measurement device for a turbine engine shaft (1) including a proof body (7) capable of being mounted on the shaft, characterized in that the proof body (7) forms a mounting for at least one acoustic-wave strain gauge (20) and is magnetized such as to allow the torque to be measured by magnetostrictive effect. The invention also relates to a method for calibrating the torque-measurement system including a first step of calibrating said device, the device being mounted on a shaft but outside of the engine, by applying reference torques to the shaft with the device and by establishing a rule regarding the relationship between the strain measured by said strain gauge and the actual torque applied, a step of mounting the shaft with the device inside the turbine engine together with placement of the magnetostrictive measurement system, the calibration of the first step being optionally reset with the engine stopped, and a step of establishing a calibration rule regarding the relationship between the torque measured by magnetostrictive effect and the reference torque provided by the strain gauges.