A magnetic sensor comprises a pair of hard magnetic films magnetized inplane in directions substantially perpendicular to the direction of a signal magnetic field and substantially equal to each other, a soft magnetic film formed in the same plane as the pair of hard magnetic films and interposed between the pair of hard magnetic films and held in contact therewith or in proximity thereto, and a signal magnetic field detecting film superposed on the main surface of the soft magnetic film. A magnetic recording-reproducing head using this reproducing head comprises the reproducing head mentioned above, a pair of magnetic pole layers vertically opposed to each other through the medium of a recording gap, and a recording head possessed of a recording track width equal to or smaller than the reproducing track width of the reproducing head. The reproducing track width L.sub.1 is so set as to satisfy the relation, L.sub.2 .ltoreq.L.sub.1