A resin composition contains a thermosetting resin (A) and an inorganic filler (B). The inorganic filler (B) includes: a first filler (B1); and a second filler (B2) of a nanometer scale having a smaller particle size than the first filler (B1). The first filler (B1) includes an anhydrous magnesium carbonate filler (b1) and an alumina filler (b2). The proportion of the first filler (B1) relative to a total solid content in the resin composition is equal to or greater than 50% by volume and equal to or less than 90% by volume. The proportion of the second filler (B2) relative to the total solid content in the resin composition is equal to or greater than 0.1% by volume and equal to or less than 2.0% by volume.