To obtain a resin composition excellent in moldability and capable of giving a cured product excellent in reliability of humidity resistance and markability with a carbon dioxide gas laser by including an epoxy resin with a phenolic resin, a cure accelerator, fused silica, and a metal complex salt dye having a specified structure.

This composition comprises an epoxy resin (e.g. bisphenol A epoxy resin) and a phenolic resin (e.g. phenol novolak resin) in amounts to give a ratio of the total number of the epoxy groups to the total number of the phenolic hydroxy groups of 0.8-1.3; a cure accelerator (e.g. triphenylphosphine); 65-90 wt.% inorganic filler (e.g. fused silica) having a mean particle diameter of at most 40 μm and a maximum particle diameter of at most 150 μm; and 0.2-2.0 wt.% metal complex salt dye. If necessary, the composition may further contain a coupling agent (e.g. silane coupling agent), a mold release (e.g. natural or synthetic wax), and a low-stress additive (e.g. silicone oil). The metal complex salt dye is a compound containing a chromium atom and four oxygen atoms arranged around the chromium atom and represented by the formula (wherein n is 2-6).