The present invention is a processing unit for processing a substrate in a casing, having: a transfer port provided in the casing through which the substrate passes when the substrate is carried into the casing by a carrier for carrying the substrate; and an inflow restricting device for controlling an atmosphere outside the casing to restrict the atmosphere from flowing into the casing through the transfer port. According to the present invention, it is possible to control the atmosphere outside the casing to restrict the atmosphere from flowing into the casing, which restricts the temperature of the substrate in the processing unit from partially varying and the temperature distribution from becoming ununiform within a plane of the substrate.