A system for synthesizing an image signal for a main scene with a plurality of image signals from image pickup devices for taking inset scenes displays the inset scenes over the main scene on a single screen. The system forms a signal representative of a drive timing for a TV inset scene camera, from a synchronizing signal in an image signal for one main scene. The TV inset scene camera is actuated by the drive timing to provide an inset scene image signal synchronizing with the synchronizing signal of the main scene. The drive timing serves to switch the main scene image signal and the inset scene image signal from one to another to synthesize another image signal. If a plurality of image pickup devices are provided remotely from each other, these image pickup devices are connected with each other through a communication line. The synchronizing signal separated from the main scene image signal is supplied to each inset scene image pickup device through the communication line while the image signal from the inset scene image pickup device without a synchronizing signal is fed to the main scene image pickup device through a common communication line.