This invention provided a magnetism detecting apparatus capable of supporting a bipolar detection wherein especially the number of elements can be reduced with a simplified circuit arrangement used. An integrated circuit (22), in which a potential at a midway of a third series circuit (34) comprising a series connection of fixed resistor elements (31,32) is used as a reference potential common tothe first and second bridge circuits (BC3, BC4), includes a first switch circuit (36) that alternately switches between a connection of a differential amplifier (35) to a first output deriving part (25) of a first series circuit (26) constituting the first bridge circuit (BC3) and a connection of the differential amplifier (35) to a second output deriving part (29) of a second series circuit (30)constituting the second bridge circuit (BC4). Thus, the invention can reduce number of components and simplify the circuit structure.