A flexible display apparatus is disclosed. The flexible display apparatus includes: a substrate on which a display unit for displaying an image, a non-display area formed outside the display unit, and at least one pad for inputting an electrical signal to the display unit are located; and a circuit board including circuit terminals to be electrically connected to the at least one pad. A stiffener including a plurality of reinforcement lines that are patterned to reduce or prevent thermal deformation of the substrate is formed on the substrate.