PURPOSE: To obtain the titled highly precise parts that is faithful to the mold, by forming from a matrix another mold using a low melting metal, casting a resin into said another mold, hardening the resin, and removing it thereby the expensive matrix can be used for a long period without being damaged.

CONSTITUTION: First, a metal, etc., is potically polished into the matrix 1 in the shape of a dach mirror array, while a low melting point metal 2 is heated to its melting point or above, and the melted metal is pressed to the matrix 1. In this state the temperature is lowered so that the shape of the dach mirror surface of the matrix 1 is transferred to the low melting point metal 2, and the metal is removed. Then a film 3 of a metal such as Ag, etc. is provided on the transferred surface of the removed low melting point metal 2 to form a mold 2', and a resin 4 such as epoxy resins is cast in the mold 2'. After the resin is hardened, the resin 4 is removed from the mold 2'. Then a reflective film 5 of Ag or the like is formed by vapor deposition method or the like on the dach mirror surface of the resin 4 to obtain the intended parts.