PURPOSE: To manufacture a vacant valve easily by inserting a core bar containing a mandrel through the center thereof into the slot of a block, forming a valve and pulling off the mandrel from the valve.
CONSTITUTION: A core bar 8 which contains a mandrel 7 made of high-tensile alloy through the center, and is made of the mixture of graphite and ceramics powder is inserted into the slot 3 of a heat-resistant steel block 4. The block 4 is subjected to the forward hot extrusion to define a stem part 11 on the block and then subjected to the hot press and the swaging to define a skirt part 15. The mandrel 7 is then pulled out from the block 4 and the core bar 8 is removed, whereby defining a hollow part 16. Thus, a vacant valve can be shaped easily.