A wound iron core formed by winding a thin strip of a soft magnetic alloy into a triodal form, characterized in that a Co-base amorphous magnetic alloy is used as the thin strip and that the thin strip is annealed in a magnetic field in the direction of excitation, so that the core exhibits a rectangle ratio Br/B 10 of 85% or higher in D.C. hysteresis curve. The Co-base amorphous magnetic alloy has a composition substantially expressed by: Co 100-a-b X a Y b where X represents one, two or more elements selected from a group consisting of Ti, V, Cr, Mn, Fe, Ni, Zr, Nb, Mo, Ru, Hf, Ta, W, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy, while Y represents one, two or more elements selected from a group consisting of B, C, Al, Si, P and Ge, and wherein the following conditions are met: 0≦ a ≦15 (atom%) and 14≦ b ≦30 (atom%).