A torque sensor has a magnetic sensor, which is composed of a first magnetic detecting element, a second magnetic detecting element and a comparator. The first magnetic detecting element outputs an output signal of a provisional detection value, while the second magnetic detecting element outputs an output signal of a reference value. The comparator compares the provisional detection value and the reference value and outputs the provisional detection value as an authorized detection value, when a difference value between the provisional detection value and the reference value is smaller than a predetermined threshold value.