PURPOSE: To obtain a composite ferrite core to be used for a transformer and an inductor which can be operated in a high frequency range for large power.

CONSTITUTION: A primary winding 5 and a secondary winding 3 are provided through an insulating spacer 4, and formed of copper foils on an insulation sheet formed by molding normal windings or a printing method. A ferrite core 8 is formed by once sintering and then connecting double the sintered elements. In the case of connecting, adhesive or adhesive in which fine ferrite particles are dispersed is used so as to reduce leakage of a magnetic flux. Ni-Zn ferrite 6 having excellent high frequency characteristics is used as an inner core, and Mn-Zn ferrite 7 having large saturated magnetic flux density is used as an outer core.