A magneto-impedance sensor which makes it possible to further improve the accuracy of external magnetic field measurement includes a magneto-impedance element, a detection circuit, a magneto-sensitive body wiring line and a conductive layer wiring line. The magneto-impedance element includes a magneto-sensitive body and a conductive layer adjacent to the magneto-sensitive body. The magneto-sensitive body and the conductive layer pass a current therethrough in the opposite directions. The magneto-sensitive body wiring line and the conductive layer wiring line are electrically connected to the magneto-sensitive body and the conductive layer, respectively. A detection coil and a detection circuit of the magneto-impedance element are electrically connected to each other through detecting conductive wires. At least parts of these lines are adjacent to each other and allow a current to pass therethrough in opposite directions.