A magnetic field detecting sensor includes a bridge circuit which is connected to multiple magnetoresistive effect elements and is capable of outputting a differential voltage between specified connection points, a magnetic field generating conductor for providing the magnetoresistive effect elements with a magnetic field in a direction opposite to that of the detection magnetic field by disposing a magnetic body near the center of the bridge circuit, a differential operation circuit which the differential voltage is input in and makes a feedback current flow to the magnetic field generating conductor, wherein the feedback current generates the magnetic field in a direction opposite to that of the detection magnetic field in the magnetic field generating conductor, and a voltage converting circuit for outputting the feedback current as a voltage value. The magnetic field generating conductor and the magnetoresistive effect elements are formed in the same stacked body.