To provide an amorphous soft magnetic alloy having a supercooled liquid region and excellent in amorphous-forming ability and soft magnetic properties, by selecting and optimizing an alloy composition, and to further provide a ribbon, a powder, a high-frequency magnetic core, and a bulk member each using such an amorphous soft magnetic alloy. The amorphous soft magnetic alloy has a composition expressed by a formula of (Fe1-αTMα)100-w-x-y-zPwBxLySiz, wherein unavoidable impurities are contained, TM is at least one selected from Co and Ni, L is at least one selected from the group consisting of Al, V, Cr, Y, Zr, Mo, Nb, Ta, and W, 0≦α0.98, 2≦w≦16 at %, 2≦x≦16 at %, 0<y≦10 at %, and 0≦z≦8 at %).