A thermosetting composition for injection molding comprising: (A) a compound represented by the following formula (A2) or (A3), and (B) a thermal polymerization initiator; wherein the composition further comprises no (G) titanium oxide or comprises (G) titanium oxide, when the composition comprises the component (G), the content of the component (G) is 5 parts by mass or less, based on a total of 100 parts by mass of components other than the component (B) and the component (C); and the composition comprises no polybutadiene di(meth)acrylate: ##STR00001##