Abstract: A noise filter includes an annular magnetic core made of a soft magnetic alloy ribbon mainly made of Fe and containing B and at least one element selected from a group consisting of Ti, Zr, Hf, Nb, Ta, Mo and W, at least 50% of the soft magnetic alloy structure being composed of body-centered cubic structured fine grains having an average grain size of 30 nm or below, a casing for accommodating the magnetic core and having an insulating plate, a pair of coils separated from each other by the insulating plate, and an electronic circuit for connecting a core element made up of the magnetic core, the casing and the coils.