PURPOSE: To mold a resin molding with a hollow part on the peripheral edge part of a windowpane without causing such defects of appearance as sink marks, burrs, warpage and deformation and with a sufficient rigidity, obviate complicated discarding work of a runner loss an each molding, improve the workability and shorten the molding cycle.

CONSTITUTION: Gas is injected into a resin molding 3 being till under molten state in a cavity 11 from a gas needle provided in the cavity 11 and a sprue 9, a manifold 10 forming runners 7 and 8 and a switch gate 13 part integrated therewith are heated by means of a heater 16 and a resin molding 3 with a hollow part is molded while the resin 12 in the runners 7 and 8 and the spure 9 is kept under molten state.