A magnetic detecting device and a method of manufacturing the magnetic detecting device are provided. Non-magnetic material layer-side magnetic layers of second fixed magnetic layers form a fixed magnetic layer. Each of the non-magnetic material layer-side magnetic layers and a free magnetic layer is formed of a layer, for example, a CoMnGeCu layer. In the CoMnGeCu layer, a bulk scattering coefficient may become larger, as compared with a CoMnGe layer. As a result, it is possible to increase the product between a magnetoresistance variation and a device area. Further, the ferromagnetic coupling magnetic field can be decreased. The Cu is added by a range which is larger than 0 at. % and not more than 17.5 at. % (average composition ratio).