To reduce the time required before a product filling operation or the time between productions. There is provided a sterilization process transition method of switching from an SIP process to a product sterilization process in a product filling apparatus that includes product supply piping that feeds a product into a filling machine through a heating sterilization part, the SIP process being intended to sterilize the product supply piping in advance before a product filling operation, and the product sterilization process being intended to sterilize the product to be filled, wherein an F value is calculated from temperature data and flowrate data on a fluid flowing in the heating sterilization part that are obtained from a plurality of temperature sensors and flowmeters disposed at arbitrary positions in the product filling apparatus at predetermined time intervals, and the temperature and flowrate at two or more of the plurality of predetermined positions in the product filling apparatus are adjusted from a
