PURPOSE: To obtain the title molding excellent in heat resistance and suitable as a large molding such as an automobile member, by simultaneously performing polymerization and molding of a monomer feed comprising a specified adduct or its mixture with other metathesis-polymerizable monomers in the presence of a metathesis polymerization catalyst system.

CONSTITUTION: A monomer feed (A) comprising a 1:1 adduct of formulas II and III, formed by performing a Diels-Alder reaction of 3a,4,7,7a- tetrahydroindene (a) of formula I with cyclopentadiene (b) or its mixture with 0W95mol% at least one metathesis-polymerizable monomer selected from among a cycloalkene except cyclohexene, a compound having at least a norbornene skeleton of formula IV (wherein the dotted valence bonds may be combined together through other atoms to form cyclic structures, etc.) is bulk-polymerized in a mold in the presence of a metathesis polymerization catalyst system (B) comprising a base catalyst component (e.g., WCl6) and an activator component [e.g., (C2H5)2AlCl] to perform polymerization and molding simultaneously.