PURPOSE: To provide the titled composition scarcely forming ionic or hydrolyzable chlorine and excellent in moisture resistance, containing an epoxy resin, a novolak phenolic resin, magnesium aluminum oxide, and an inorganic filler.

CONSTITUTION: A composition containing an epoxy resin, (B) a novolak phenolic resin, magnesium aluminum oxide of the formula (wherein n, m, and X are each ≥0.1 integer), and an inorganic filler, wherein said filler is contained in an amount of 25W90wt%, based on the resin composition. The mixing ratio of the novolak phenolic resin is preferably such that the molar ratio of the epoxy groups in the epoxy resin to the phenolic hydroxyl groups in the novolak phenolic resin falls within the range of 0.1W10. the magnesium aluminum oxide used can be obtained by calcining hydrotalcite, for example.