A high power inductance device enables a large ferrite magnetic core to be manufactured at low cost and with ease and improves heat radiation efficiency to reduce an increase in the temperature of the core. The inductance device has a ferrite magnetic core and a winding wire wound around the ferrite magnetic core and is mounted on a heat radiation structure through at least one of the front surfaces of the ferrite magnetic core. The ferrite magnetic core is made of a core aggregate obtained by arranging side by side a plurality of ferrite cores 10 having a completely-closed magnetic path structure or a quasi-closed magnetic path structure with a magnetic gap such that an interval is placed between the ferrite cores and magnetic paths are parallel to each other. The inductance device is mounted such that at least one plane surface of the peripheral surfaces of each of the ferrite cores is brought into direct or indirect contact with the heat radiation structure 18 with a metal plate 12 inserted into the interval between the ferrite cores and the common winding wire 14 wound around all the ferrite cores.