To provide a highly reliable torque sensor capable of determining failures in a torque detecting circuit.
An A.C. voltage Vosc is impressed on detecting coils 13 and 14, and the voltages which appear at both ends of the coils are inputted to the input-side (+) terminal and (-) terminal of an operational amplifier OP1. Its output is rectified by a synchronous detector SR and outputted as a torque signal. A second monitoring part 25b constituted of comparators CP1 and CP2 and transistors TR1 and TR2 is provided for detecting reductions in the amplitude of the A.C. voltage Vosc supplied for the detecting coils. Different reference voltages are inputted to the CP1 and CP2 in operation mode and test mode to determine whether the amplitude of the A.C. voltage Vosc is normal or not in the operation mode and to verify whether an anomalous state can be detected or not in the test mode by setting a higher reference voltage than in normal times at the second monitoring part 25b and intentionally setting the anomalous state.
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