A flexible battery is disclosed. The flexible battery can include: an electrode assembly; and an exterior material in which the electrode assembly is encapsulated together with an electrolyte, in which the electrode assembly and the exterior material are formed such that patterns for contraction and extension in a longitudinal direction have the same directionality when the flexible battery is bent. As such, the patterns for contraction and extension in the longitudinal direction are formed on both of the exterior material and the electrode assembly, thereby preventing or minimizing deterioration in the physical properties even though the flexible battery is bent.