A soft magnetic under layer has a low antiferromagnetic coupling force and a high saturation magnetic flux density. The soft magnetic under layer includes two soft magnetic layers and a spacer layer. The soft magnetic layers are expressed by a composition formula as (Fe100-XCoX)100-Y-MY by atomic ratio, wherein 15≦X≦30, 10≦Y≦30, and an element M is at least one element selected from a group of Ta, Ti, Zr, Nb, Cr, and B; are composed of residual incidental impurities; and each have a thickness of 10 to 50 nm. The spacer layer is composed of one element selected from a group of Ru, Cr, Cu, Re, and Rh and has a thickness of 0.10 to 0.50 nm. The soft magnetic layers are antiferromagnetically coupled through the spacer layer inserted therebetween. An antiferromagnetic coupling force between the soft magnetic layers is 100 to 4,000 A/m.