Problem to be solved. To provide a novel treatment environment stabilization device capable of strictly managing temperature for each of treatment zones having different treatment temperatures in a pasteurizer for performing heating sterilization treatment on treatment objects such as containers filled with beverage. Solution. A treatment environment stabilization device 10 comprises: a thermal shield guide plate 11 being provided in a lower part of a nozzle unit 3 for receiving treatment water W sprayed from a nozzle unit 3 and then causing the treatment water to flow downward in the form of a water screen like a waterfall, at a boundary part between treatment zones of a pasteurizer 1 having different treatment temperatures, for example at a boundary part between a sterilization zone Z2 and a cooling zone Z3, or at a boundary part between a temperature rise zone Z1 and the sterilization zone Z2, thus maintaining an atmospheric temperature...
