To provide a throwing device, a throwing slot cover and a throwing method that can prevent a throwing object from being exposed to outside air and scattered when the object is thrown into a vessel with a simple configuration at low cost.

This throwing slot cover 1 includes working space 1a formed on a throwing slot 11 on a vessel 10, where a worker can insert his hands through glove ports 3 from outside and throw in throwing objects in a sealed condition and a connection port for communicating the work space 1a and the throwing slot 11 with each other. The throwing slot cover 1 is so configured that the cover 1 is mounted on the slot 11 of the vessel 10 in a manner that the slot 11 and the working space 1a are communicated with each other.