An extendable signboard is provided to implement an air signboard on an exterior of a building by preventing the signboard from being pulled down by changing a length of the signboard. An extendable signboard comprises a main body(100), a folding mount(200), and an elastic member(300). The main body includes a driver and a slot-type sliding unit. The folding mount has plural X-like structures. Middle connection nodes between the X-like structures are coupled with each other using a center hinge, while end connection nodes are coupled using an end hinge. A sliding member couples an end portion of one link member with the sliding unit. The elastic member is coupled with the folding mount. An advertisement is printed on the elastic member. The driving unit pushes the center hinge in an arrangement direction of the link member.
