A spherical inorganic oxide powder wherein a volume-based cumulative 50% diameter D50 is 4-55 μm; and in a cross-section of a cured body containing an epoxy resin and the spherical inorganic oxide powder at a mass ratio of 2:1, when a total of 5000 particles with a maximum diameter of 51 μm or larger are observed in a field of view at 100× magnification using a scanning electron microscope, a total number of air bubbles having a maximum diameter of 1 μm or larger and smaller than 10 μm is 40 or fewer and a total number of air bubbles having a maximum diameter of 10 μm or larger is 30 or fewer.