In a sterilization treatment line in which an upstream side tank 16 in which product liquid is stored and a downstream side tank 17 are connected to each other through a conduit 18 through which the product liquid is transferred, a high-temperature heating unit 21 for sterilizing the product liquid is provided at an intermediate portion of the conduit, one or more stages of heating units 22, 23 heating the product conduit in a stepwise manner are provided for the conduit at portions between the upstream side tank and the high-temperature heating unit, and one or more stages of cooling units 24, 25, 26 cooling the product conduit in a stepwise manner are provided for the conduit at portions between the high-temperature heating unit and the downstream side tank, a plurality of intermediate piping lines P, Q are arranged in parallel with each other at portions between a heating stage of the heating unit 23 disposed in a temperature range at which the product liquid is burnt and between a cooling stage of the cooling unit 24 disposed in a temperature range at which the product liquid is burnt, and a sterilization treatment, a CIP treatment and a positive pressure keeping treatment with respect to the product liquid to be transferred from the upstream side tank to the downstream side tank are performed by switching the plural intermediate piping lines arranged in parallel with each other.
