1. An expandable display device comprising:a housing comprising a fixing portion;
a pair of sliding portions provided at respective sides of the fixing portion, each of the sliding portions being configured to be drawn out from the housing along a first direction such that a distance from the respective sliding portion to the fixing portion is changed; and
a panel unit comprising:
a flexible display panel comprising a plurality of pixels and having a screen at a first side thereof; and
a support panel attached to a second side of the flexible display panel facing the first side, the support panel comprising a plurality of slits extending in a second direction crossing the first direction.