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Characteristics of a magnetostrictive torque sensor were studied in the excitation current range 10~1000 mA and at excitation frequencies from 1 kHz to 100 kHz. Ni-Cr-Mo steel (JIS standard SNCM439) ferromagnetic material was used in an experimental shaft because of its high mechanical strength under applied torques ranging - 1500~1500 Nm. As the excitation current was increased, the sensor sensitivity was markedly enhanced and the hysteresis and offset deviation along the shaft circumference were reduced. Good sensor output has been obtained at large excitation currents exceeding 200 mA. In addition, a new memory phenomenon, which seems to consist of changes in magnetic domains induced by torque-generated stresses, has been discovered in the small excitation current range.