To provide a method for manufacturing an insulating material containing a magnetic material, which allows the insulating material to obtain an effect of increasing magnetic permeability without relatively increasing a concentration of the magnetic material mixed in the insulating material, allows the insulating material containing the magnetic material obtained by the method to be applied to a circuit bord to enhance characteristic impedance, and thereby provides an effect of reducing power consumption to the insulating material.

The insulating material containing the magnetic material is obtained by the manufacturing steps which comprise: mixing a resin varnish and slurry in which the magnetic material is dispersed in a solvent; and applying, drying and baking the mixture. The slurry producing step comprises: a step of producing a dispersion solvent in which a surface active agent is added to the solvent; and a step of mixing fine powders of the magnetic material with the dispersion solvent. The mixing step of the fine powders of the magnetic material comprises: a step of stirring an aggregate with a screw; a step of irradiating the aggregate with ultrasonic waves having a frequency of less than 100 kHz; and a step of irradiating the aggregate with ultrasonic waves having a frequency of 100 kHz or more.