An amorphous soft magnetic alloy powder which is produced by a water atomization method is provided. The powder contains an amorphous phase having a temperature interval .DELTA.Tx of a supercooled liquid of 20K or more; having a hardness Hv of 1000 or less; is provided with a layer with a high concentration of Si at a surface portion thereof; and being represented by the following composition formula: Fe.sub.100-a-b-x-y-z-w-tCO.sub.aNi.sub.bM.sub.xP.sub.yC.sub.zB.sub.wSi.su- b.t And M is one or two or more elements selected from Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Pt, Pd, and Au.