Magnetism detecting apparatus and magnetic material identifying apparatus using the same

A detecting apparatus for reading the magnetic strip on a card compensates for coercivity variations by employing two magnetizing coils wound in opposite senses on the magnetic poles and two detecting coils coupled to the magnetizing coils and which are also wound in opposite sense on the magnetic poles. Differential output from the detecting coils represents a shift from normal in the coercivity or permeability of the magnetic strip so as to permit compensation for shifts due to factors such as a warped card or dust intervening thereby permitting accurately identifying whether or not the magnetic strip on the card is a high coercive force type or a low coercive force type.