PURPOSE: To provide the titled compound which gives beautiful moldings on a mass production scale, which are free from color non-uniformity and have very high transparency and good surface smoothness, containing a three-dimen sional styrene polymer and glass powder.

CONSTITUTION: The titled compound is obtd. by incorporating 1W20pts.wt. three-dimensional styrene polymer (A) (e.g., a polymer having a crosslink density of 2W30% obtd. by adding divinylbenzene to styrene monomer and carrying out a crosslinking reaction) and 10W200pts.wt. glass powder (B) (pref. powder having an average particle size of 80W200 mesh) in 100pts.wt. unsaturated polyes ter resin (C). When the compound is compressed by heating, the resin component is prevented from shrinking during curing so that beautiful moldings can be obtd. which are free from color non-uniformity and have good surface smooth ness and transparency.