To solve the following problems: in a windowpane with a frame, an insert component for decorating or reinforcing the frame is fixed by a fixing pin in the cavity of a mold used to injection-mold the frame, but the part of the fixing pin of the frame becomes a hollow after the frame is molded to spoil the appearance and to cause defective water-tightness in the window frame.

The frame is molded to be integrated with the windowpane through a process in which the windowpane is set in the mold, a process in which the insert component is fixed to the cavity of the mold for injection molding by the fixing pin, a process in which a resin for forming the frame is injected into the cavity, a process in which after the injection of the resin is started, the entire fixing pin for fixing the insert component is moved from the cavity to an upper mold or a lower mold before the end of the resin injection, and a process in which the windowpane is taken out from the mold after the end of the resin injection.