Conventionally, as a geomagnetic sensor that measures the earth magnetism, a flux gate type (FG type) geomagnetic sensor is known widely (for example, refer to Patent Literature 1). 
Although being capable of high precision measurement of the earth magnetism, the flux gate type geomagnetic sensor has a problem in that, because a core with an exciting coil wound therearound has to be magnetically saturated with an AC current, namely an alternating current, the excitation current increases and power consumption is large.