To provide a current sensor capable of inhibiting the occurrence of a bit error as much as possible at every conversion between analog data and digital data.

A battery ECU 8 is built in a resin case 10 of a current sensor 7 such that a voltage (analog data) from a hall element 16 is converted and processed into digital data by A/D conversion in the battery ECU 8. With that construction, a conversion between analog data and digital data needs to be performed only once, and a bit error accompanying a plurality of conversions can be reduced in the traditional way.