A magnetic detecting element capable of maintaining a large .DELTA.RA and reducing magnetostriction by changing a material of a free magnetic layer, and a method of manufacturing the same is provided. A CoMnXZ alloy layer or CoMnXRh alloy layer is formed in a free magnetic layer where an element X is at least one or two elements of Ge, Ga, In, Si, Pb, and Zn, and an element X in the latter case is at least one or two elements of Ge, Ga, In, Si, Pb, Zn, Sn, Al, and Sb. By forming the CoMnXZ alloy layer or the CoMnXRh alloy layer in the free magnetic layer, the magnetostriction of the free magnetic layer can be reduced while maintaining the large .DELTA.RA, compared with a case where only the CoMnX alloy is formed.