Plug-closing processing units are provided with: a first plug chuck parts that grasp plugs; and a second plug chuck part located above the first plug chuck parts, wherein the first plug chuck parts each include at least two first supports that grasp the plugs from more than one direction, and the second plug chuck part is provided with a plug-closing mechanism that includes a second support disposed in the radial direction of plugs and having an inclined lower end surface. Thus, provided are a plug processing device capable of stable plug-opening processing and plug-closing processing on a conveyor line for a specimen container, and a specimen test automation system including the plug processing device.