A flexible display device includes a base support of structurally flexible, a flexible display which is supported by and bendable with the base support, and at least one positioning mechanism disposed leftward or rightward of the base support. The positioning mechanism includes two mounts which are mounted to two support plates of the base support, a plurality of hinge bodies which are structurally flexible with a support rib unit of the base support, and a leaf spring unit extending through inside of the hinge bodies to terminate at a first spring end secured in one of the mounts, and a second spring end which is releasably and frictionally engaged inside the other one of the mounts by virtue of a sliding block and a spring-loaded unit.