PURPOSE: To form a hollow part of any shape within a molding easily by a method whereby said hollow part is preliminarily formed by using an alloy melting at a relatively low temperature, fitted in a die, formed of a thermosetting resin before said alloy is melted by heat.

CONSTITUTION: For example, a hollow part 3 of a valve component for liquid use is formed of an alloy melting at a low temperature through casting or die casting. If it is further desired that a metallic component or the like is incorporated into the valve component permanently through insert molding, this component 4 is mounted in the molding of the alloy or die. The adjusted metallic component is fixed at a given position in a plastic die. Then, for example, an epoxy resin blended with a thermosetting agent is injected into the die in a manner not to generate air bubbles. After the resin is set, the resultant molding is taken out, and heated in a heating furnace. Since the epoxy resin is resistive to the temperature 80 to 160°C, the metallic component in which the hollow part is formed is formed of an alloy melting in this temperature range.