A method of sterilizing a filling nozzle, wherein a hot water or a liquid chemical agent heated to a predetermined temperature is fed to drink supply piping that feeds a drink to a plurality of filling nozzles at the same time, a flow rate of the hot water or the liquid chemical agent is detected at all the filling nozzles while the hot water or the liquid chemical agent is being discharged from all the filling nozzles, wherein a representative temperature of the hot water or the liquid chemical agent downstream of at least one filling nozzle is measured, an F value is calculated based on the representative temperature, and a sterilization process is ended when both the flow rate at each filling nozzle and the F value calculated based on the representative temperature reach respective target values, a cup is placed on a nozzle mouth of each filling nozzle and a drain pipe formed by a flexible pipe is connected to the cup, the drain pipe is provided with a temperature sensor, a return pipe extends from the drain pipe to a manifold valve and the return pipe is provided with a heater, information about the representative temperature measured by the temperature sensor is transmitted to a controller, the controller compares the representative temperature measured with a reference temperature and provides a predetermined output, the hot water or the chemical agent is introduced into an annular flow path formed by the drink supply piping, the drain pipe and the return pipe, is circulated in the annular flow path, and is heated to the predetermined temperature by the heater provided on the return pipe, and the hot water or the chemical agent sterilizes an interior of the filling nozzles and an interior of a filler. a flow rate of the hot water or the liquid chemical agent is detected at all the filling nozzles while the hot water or the liquid chemical agent is being discharged from all the filling nozzles, wherein a representative temperature of the hot water or the liquid chemical agent downstream of at least one filling nozzle is measured, an F value is calculated based on the representative temperature, and a sterilization process is ended when both the flow rate at each filling nozzle and the F value calculated based on the representative temperature reach respective target values, a cup is placed on a nozzle mouth of each filling nozzle and a drain pipe formed by a flexible pipe is connected to the cup, the drain pipe is provided with a temperature sensor, a return pipe extends from the drain pipe to a manifold valve and the return pipe is provided with a heater, information about the representative temperature measured by the temperature sensor is transmitted to a controller, the controller compares the representative temperature measured with a reference temperature and provides a predetermined output, the hot water or the chemical agent is introduced into an annular flow path formed by the drink supply piping, the drain pipe and the return pipe, is circulated in the annular flow path, and is heated to the predetermined temperature by the heater provided on the return pipe, and the hot water or the chemical agent sterilizes an interior of the filling nozzles and an interior of a filler.