A magnetic sensor in which magnetic characteristics are stabilized extremely by taking account of the contact area between an underlying layer of a magnetic body and a semiconductor substrate. On the semiconductor substrate (11), a plurality of Hall elements (12a, 12b) are provided while being embedded in flush with the surface of the semiconductor substrate and spaced apart by a predetermined distance. On the Hall element and the semiconductor substrate, an underlying layer (14) composed of a metal or resin and having a coefficient of thermal expansion different from that of the plurality ofHall elements and an area at least partially covering the region of the plurality of Hall elements is provided through a protective film (15). On the underlying layer, a magnetism convergence plate (15) having a magnetism amplification function of larger area than that of the underlying layer is provided. Generation of offset voltage is suppressed by reducing the contact area between the underlying layer of magnetic body and the semiconductor substrate.