The present disclosure relates to a flexible display device case that is mounted to a flexible display device including a first body and a second body configured to be movable relative to the first body, and including a first member mounted to the first body to surround a side surface portion of the first body, and a second member mounted to the second body to surround a side surface portion of the second body, wherein an area overlapped by the first member and the second member changes as the first body and the second body move relative to each other.