PURPOSE: To enhance precision and to lower cost by fitting a pair of right and left holding nestings to the parts correspondent to the once-through hold of a valve body and holding the nestings at the specified interval in the top and bottom forces and force-feeding molten resin from a sprue rocket part.

CONSTITUTION: A valve body 2 is fitted to the inside of a female mold of a top force 1a. In other words, a valve rod part 2b is inserted into a valve rod insertion hole 3 and also the stepped projections 8b of the holding body 2 from the right and left side parts so that the whole body is held at the specified interval in the mold. In this state, the top and bottom forces are mated and allowed to coincide with each other and fixed and also the tip of the valve rod part 2b is stopped by a holder 4 and fixed. Resin liquid is force-fed into the above-mentioned interval from the sprue rocket 6 of the bottom force. After resin is solidified, both the top force 1a and the bottom force 1b are opened and a valve box is taken out and the right and left holding nestings 8 are rotated and drawn.