A sterilization process transition method of switching from an SIP process to a product sterilization process in an apparatus including piping that feeds a product into a filling machine through a heating sterilization part. The process sterilizes the piping before a filling operation, and the product sterilization process sterilizes the product to be filled. An F value is calculated from temperature and flowrate data on a fluid flowing in the heating sterilization part that are obtained from temperature sensors and flowmeters disposed in the product filling apparatus at predetermined time intervals. The temperature and flowrate at two or more predetermined positions in the product filling apparatus are adjusted from a set temperature and a set flowrate for the SIP process to a set temperature and a set flowrate for the product sterilization process while preventing the F value from becoming lower than a predetermined value.
