The present invention provides a powder magnetic core which has a low iron loss and an excellent constancy of magnetic permeability and is suitably used as a core for a reactor mounted on a vehicle. The powder magnetic core is a compact of a mixed powder containing an iron-based soft magnetic powder having an electrical insulating coating formed on its surface and a powder of a low magnetic permeability material having a heat-resistant temperature of 700° C. or higher than 700° C. and a relative magnetic permeability of not more than 1.0000004. The density of the compact is 6.7 Mg/m3 or more, and the low magnetic permeability material exists in the gap among the soft magnetic powder particles in the green compact.