In a sterilizing method for a drink filling system provided with a drink supply pipe line (7) for feeding drink into a filling machine (2) through a heating sterilizing section (18), wherein hot water or heated steam is fed to the drink supply pipe line (7), F-values are calculated while detecting temperature at a plurality portions of the drink supply pipe line at every predetermined time interval, and a sterilizing process is ended at a time when a minimum F-value reaches an aimed value. According to such method, a working time till the starting of drink filling work or a producing interval time can be shortened.