To improve the insulation property and raise the safety of a noise filter which has a cable passage hole in the magnetic core, provided with an insulating armor material.

This noise filter comprises a magnetic core 1 consisting of a pair of magnetic core members 11 and 12 and in which a closed magnetic path and a cable passage hole are made, when a pair of magnetic core members 11 and 12 are jointed together at each junction face 2 and 2, and insulating armor materials 51 and 52 severally provided at the external surfaces of the magnetic core members 11 and 12 in a pair. In this case, the filter has insulating interior materials 8 and 8 for covering recesses 3 of the magnetic core members 11 and 12 as a pair, between which a cable passage hole is made by a junction.