A thermosetting epoxy resin composition comprising (A) a reaction mixture of a triazine derivative epoxy resin and an acid anhydride at a ratio of the epoxy group equivalent to the acid anhydride equivalent of 0.6 to 2.0; (B) an internal mold release agent; (C) a reflective material; (D) an inorganic filler; and (E) a curing catalyst. The internal mold release agent of component (B) comprises a carboxylate ester represented by: R11—COO—R12  (1) wherein R11 and R12 are CnH2n+1 and n is 1 to 30 and a compound represented by: wherein R1, R2, and R3 are selected from H, —OH, —OR, and —OCOCaHb with the proviso that at least one includes —OCOCaHb; R is CnH2n+1 (wherein n is an integer of 1 to 30), a is 10 to 30, and b is 17 to 61.