PURPOSE: To read sufficiently high-frequency magnetic recording by using a magnetic which provides excellent Faraday rotation such as Y. I. G as a magnetic material, and further detecting electrically an electric signal which is increased or decreased by its effect, by another signal switching device.

CONSTITUTION: The electic power wave of a carrier signal source 1 inputted to the Y. I. G2 is a stable constant output by the influence of the magnetic field of a bias magnet 3 and increased or decreased almost in proportion to the direction or intensity of magnetism by the influence of a magnetic recording medium 4 when the mgnetic recording medium 4 approaches the Y. I. G2 to be outputted from a directional stripe line or antenna part 5 which performs cavity resonance, etc. The outputted electric signal is further converted by another signal switching device 6 to detect the direction or intensity of the magnetism of the magnetic recording medium 4 electrically. Thus, the distribution, direction, and intensity of the high-density magnetic field are detected and read of high-frequency magnetic record of MHz, GHz, etc., is facilitated, obtaining a precise magnetic field sensor which generates less noise.