A current sensor includes a magnetic sensor including magnetoresistive sensors configured to detect induction fields generated by a measurement current passing through a current line, a magnetic field application unit configured to apply to the magnetoresistive sensors a magnetic field having a direction perpendicular to sensitivity directions of the magnetoresistive sensors; and a computing unit configured to calculate from an output of the magnetic sensor a compensation value for the output. The computing unit is configured to be capable of calculating the compensation value from the outputs of the magnetic sensor obtained in at least two states in which magnetic fields applied by the magnetic field application unit are different from each other.