Provided is a flexible battery. A flexible battery according to one embodiment of the present invention comprises: an electrode assembly; and an exterior material for sealing the electrode assembly along with an electrolyte. Both the electrode assembly and the exterior material are formed such that patterns for contraction and extension with respect to the longitudinal direction have the same directionality in the event of being bent, and a region on which the patterns are formed comprises a region which satisfies a condition according to the present invention. As such, the patterns for contraction and extension with respect to the longitudinal direction are formed on both the exterior material and the electrode assembly, thereby preventing or minimizing deterioration of the required physical property even if bending occurs. Therefore, the present invention is applicable not only to wearable devices such as smart watches and watch straps, but also to various electronic devices, such as rollable displays, which require battery flexibility to be secured.