A magnetic core is provided with a plurality of iron-based soft magnetic alloy plates having a crystal structure and an average crystal grain diameter of 100 nm or less, and an insulation film provided between one and another of the plurality of iron-based soft magnetic alloy plates. The percentage of the magnetic core occupied by the plurality of iron-based soft magnetic alloy plates is 65% or more, and the initial permeability at a frequency of 100 kHz is 25,000 or more.