PURPOSE: To enable to start the title device even if the temperature of circulation water is low, by a method wherein a cutter driving shaft is made into a hollow shaft and water, whose temperature is high enough to prevent a die from supercooling, is injected through the driving shaft.

CONSTITUTION: A driving shaft 10 is made into a hollow shaft, a comparatiely small quantity of heated water (60W80°C) heated in a fluid heater is injected toward a die 8 by passing through the inside of the hollow shaft, through which molten resin to be discharged through the die 8 is kept warm so as not to cure the resin through cooling within the die. A pellet manufacturing device 1 is made to act, molten state resin is extruded into a head 6 through on opening part 7 of the die 8 and cut off in a predetermined length by a cutter 9. As the die 8 is covered with the heated water always during operation and not exposed under low-temperature main circulation water due to a matter that the heated water is being injected toward the die 8 through the driving shaft 10 of the cutter 9, it is not feared that the molten resin in the inside of the die 8 is cured.