To accurately bring an optical axis of a lens into coincidence with a central axis of a lens holder without causing a scratch within an optical effective diameter of the lens when the lens to be inserted is held by the holder and molded.

A mold for insert molding the lens includes two-divisible molds 4, 5 each having a cavity larger than an outer diameter of the lens 3 to be inserted, and lens holders 1, 2 respectively inserted in engaging state into the molds 4, 5 so as to be disposed at a substantially central part of the cavity and having ends of shapes smaller than the outer diameter of the lens for disposing the lens 3 by holding the lens 3 from both the surfaces before a resin is filled. Infinitesimal curved surfaces are formed over the entire peripheral surfaces of the ends of the holders 1, 2 brought into contact with the lens 3.