A method of synchronizing reference image with additional image in digital broadcasting includes generating at least one frame having predetermined identifier for providing notice of the start time of the reference image to receiver in advance; and transmitting at least one frame having the predetermined identifier to the receiver. Alternatively, the method of synchronizing reference image with additional image of includes generating signaling information containing additional image interlocking information at a transmission side in order to prepare for the additional image interlocked with the reference image at a reception side in advance; and providing the signaling information to the receiver. Therefore, it is possible to accurately and effectively perform the synchronization of 3D reference image with 3D additional image stored in the receiver or a streamed 3D additional image.