A current sensor for detecting a first electric current flowing through a current path includes a sensor chip, a coil, a current control circuit, and an output circuit. The sensor chip includes a magnetoresistive element and is adopted to be located near the current path. The coil applies a bias magnetic field to the magnetoresistive element. The current control circuit supplies a second electric current to the coil. The second electric current periodically changes in polarity. The output circuit outputs a difference between a first voltage and a second voltage. The first voltage is generated by the magnetoresistive element, when the second electric current flowing through the coil has a positive polarity. The second voltage is generated by the magnetoresistive element, when the second electric current flowing through the coil has a negative polarity.