A magnetic sensor comprising: a first current line, a second current line and a third current line that are disposed in parallel to each other in sequence in a width direction and electrically connected in series; and a magnetoresistive effect element disposed under the second current line and extending along a direction of extension of the second current line, the magnetoresistive effect element having an electric resistance that changes by an induced magnetic field generated by current flowing through the first current line, the second current line and the third current line, the following inequality expression being satisfied: L s / W g ≤ 5 where L s is a length from an outside of the first current line to an outside of the third current line in a width direction, and W g is a length in the width direction of the magnetoresistive effect element, further comprising a plurality of bias-magnetic-field applying current lines extending in a direction vertical to the direction of extension of the second current line, the bias-magnetic-field applying current lines being adapted to apply a bias magnetic field to the magnetoresistive effect element by an induced magnetic field generated by a flowing current, wherein the plurality of bias-magnetic-field applying current lines is disposed above the first current line, the second current line and the third current line, or wherein the plurality of bias-magnetic-field applying current lines is disposed between the second current line and the magnetoresistive effect element, or wherein the plurality of bias-magnetic-field applying current lines is disposed below the first current line, the second current line and the third current line, the magnetic sensor further comprising: a fourth current line extending in parallel to the first current line and disposed outside the first current line; a fifth current line extending in parallel to the third current line and disposed outside the third current line; characterised by a first yoke layer disposed below the fourth current line, containing a soft magnetic material, and not electrically connected to the first to fifth current lines and the magnetoresistive effect element; and a second yoke layer disposed below the fifth current line, containing a soft magnetic material, and not electrically connected to the first to fifth current lines and the magnetoresistive effect element.. a first current line, a second current line and a third current line that are disposed in parallel to each other in sequence in a width direction and electrically connected in series; and a magnetoresistive effect element disposed under the second current line and extending along a direction of extension of the second current line, the magnetoresistive effect element having an electric resistance that changes by an induced magnetic field generated by current flowing through the first current line, the second current line and the third current line, the following inequality expression being satisfied: L s / W g ≤ 5 where L s is a length from an outside of the first current line to an outside of the third current line in a width direction, and W g is a length in the width direction of the magnetoresistive effect element, further comprising a plurality of bias-magnetic-field applying current lines extending in a direction vertical to the direction of extension of the second current line, the bias-magnetic-field applying current lines being adapted to apply a bias magnetic field to the magnetoresistive effect element by an induced magnetic field generated by a flowing current, wherein the plurality of bias-magnetic-field applying current lines is disposed above the first current line, the second current line and the third current line, or wherein the plurality of bias-magnetic-field applying current lines is disposed between the second current line and the magnetoresistive effect element, or wherein the plurality of bias-magnetic-field applying current lines is disposed below the first current line, the second current line and the third current line, the magnetic sensor further comprising: a fourth current line extending in parallel to the first current line and disposed outside the first current line; a fifth current line extending in parallel to the third current line and disposed outside the third current line; characterised by a first yoke layer disposed below the fourth current line, containing a soft magnetic material, and not electrically connected to the first to fifth current lines and the magnetoresistive effect element; and a second yoke layer disposed below the fifth current line, containing a soft magnetic material, and not electrically connected to the first to fifth current lines and the magnetoresistive effect element.. a fourth current line extending in parallel to the first current line and disposed outside the first current line; a fifth current line extending in parallel to the third current line and disposed outside the third current line; characterised by a first yoke layer disposed below the fourth current line, containing a soft magnetic material, and not electrically connected to the first to fifth current lines and the magnetoresistive effect element; and a second yoke layer disposed below the fifth current line, containing a soft magnetic material, and not electrically connected to the first to fifth current lines and the magnetoresistive effect element..