The present invention relates to a thermosetting resin composition that contains a thermosetting resin and an inorganic filler. The thermosetting resin contains a curing agent. A solution of methyl ethyl ketone containing 3% by weight of the curing agent has a Gardner color scale of 15 or more. The amount of curing agent contained is 10% by weight or more based on the total solids content of the thermosetting resin composition.