1. A printed wiring board comprising:a sheet-shaped core base material containing a plurality of magnetic material layers which each contains a magnetic material;
a coil disposed inside the core base material containing the plurality of magnetic material layers; and
an external circuit layer disposed on at least one of first and second external surfaces of the core base material containing the plurality of magnetic material layers opposite to each other,
wherein adjacent magnetic material layers directly contact each other throughout the core base material from the first external surface to the second external surface, and
the coil has a conductive part and an insulating film covering the conductive part.