To accurately detect only isotropic external magnetic field intensity and attain detecting the external magnetic field which is very fine, by forming a narrow line type magnetoresistance effect element (MR element), as a closed loop of rotation symmetry.

This magnetic sensor is constituted by forming an MR element 2 and a wiring part 3 in a film on a nonmagnetic substrate 1 by a vacuum thin film forming technique. The wiring part 3 is constituted of conductor electrically connected with the MR element 2 which is formed in a narrow line constituting a close loop of rotation symmetry. The MR element 2 is arranged isotropicaly to an external magnetic field H. When the external magnetic field H changes, the resistance value of the MR element 2 changes, so that magnetoelectric conversion is generated by supplying a constant sense current to the MR element 2 through wiring part 3 from output terminals. Since the MR element 2 is isotropically arranged, the angle between the sense current flowing in the MR element 2 and the external magnetic field H is constant independently of the external magnetic field H.