The present invention relates to a magnetic sensor with which magnetic characteristics are made extremely stable by consideration of an area of contact of a base layer of a magnetic substance and a semiconductor substrate. On a semiconductor substrate (111) a plurality of Hall elements (112a, 112b) are embedded so as to be coplanar to a top surface of the semiconductor substrate while being mutually spaced apart by a predetermined distance, and above the Hall elements and the semiconductor substrate, a base layer (114), having coefficient of thermal expansion differing from that of the Hall elements and partially covers a region of each Hall elements, is formed via a protective layer (113), and a magnetic flux concentrator (115), having an area larger than the base layer and with magnetic amplification, is formed on the base layer. An area of contact of the base layer of the magnetic substance and the semiconductor substrate is made small to lessen the generation of an offset voltage.