The present invention is such a plug application and removal device that mist which is generated upon plug removal of a sample container or a reagent container is not peripherally scattered, or is such a sample processing device that mist which is generated upon dispensing of a sample or a reagent into a container is not mixed to another container. A plug application and removal device has a container holding mechanism that holds a container housing liquid inside and applied with a plug, and has a plug application and removal mechanism that removes or applies the plug from/to the container. The plug application and removal device has: a control mechanism for controlling movement of liquid or mist spilled out of the container upon a process of removal or application of the plug by the plug application and removal mechanism.