To improve measuring accuracy, to dispense with necessity of a secondary coil for allowing second current to flow, and to decrease the size.

A ferromagnetic body magneto-resistive element unit 10 and an operational amplifying circuit unit 20 are formed on the same chip, individual magneto-resistive bodies 11 to 14 are formed into bridge shapes in the ferromagnetic body magnetoresistance element unit 10, at least one of magneto-resistive bodies has a resistance value different from a resistance value of the other magneto-resistive body, and therefore, the magnetic balancing state can be naturally formed in supplying of the stationary current. Since any hall element is not used as in the past, the change by the temperature is not generated, and the measuring accuracy is high, and any secondary coil for allowing secondary current to flow, which has been required for the magnetic balance in the past, is not required.