PURPOSE: To prevent leakage of chemical fluid, with which an injector main unit is filled, by sterilizing an injector and the chemical fluid while adjusting a pressure in a sterilizer in a manner wherein the pressure in the sterilizer is obtained almost equal to a pressure in the chemical fluid-filled injector absorbed in the sterilizer.

CONSTITUTION: In the case of sterilizing a chemical fluid-filled injector, a temperature of chemical fluid and a pressure in a sterilizer are set as shown in the table 1, and in accordance with this preset value, the pressure in the sterilizer is adjusted by a controller so as to obtain the pressure in the sterilizer almost equal to the pressure in an injector main unit 1. That is, because a fixed relation is provided between a temperature rise in the sterilizer and a temperature rise of the chemical fluid in the injector main unit 1 (the temperature rise of the chemical fluid is delayed little by little from the temperature rise in the sterilizer), this relation is experimentally obtained while controlling the temperature of the chemical fluid and the temperature in the sterilizer so as to obtain the relation as shown in the table 1, when the temperature and pressure in the sterilizer are increased, sterilization work of the chemical fluid can be performed with a piston member 4 fitted into the injector main unit 1, left without moving.