To obtain the subject composition having excellent moldability, soldering resistance, etc., by using respectively specific epoxy resin, phenolic resin hardener, brominated epoxy resin, antimony oxide, inorganic ion exchanging material, fused silica powder and cure accelerator as essential components.

This composition contains (A) an epoxy resin containing ≥30wt.% (based on the total epoxy resin) of an epoxy compound of the formula (R is H, a 1-9C alkyl, etc.), (B) a phenolic resin hardener having a melt viscosity of ≤5 poise at 150°C, (C) a brominated epoxy resin, (D) antimony oxide, (E) at least one inorganic ion exchange material selected from hydrated bismuth oxide and hydrotalcite compound, (F) fused silica powder and (G) a cure accelerator as essential components. The composition satisfies the formulas 0.2<a/b<3.0, 0.03<(a+b)/R≤0.2 and 0.05<c/(a+b)≤3 wherein R is the total weight of the compounded components A to C, (a) is the weight of bromine in the component C, (b) is the weight of antimony in the component D and (c) is the compounding weight of the component E.