The external device, for example, an electronic flash device, is wirelessly connectable to an information communication device, for example, a camera. The external device includes: a synchronization data creation unit that outputs synchronization data for synchronization of timing of processing related to photography; a packet creation unit that creates a communication packet including control information; and a packet output unit that outputs the communication packet to the exterior by wireless communication. The packet creation unit includes a packet reception unit that receives the communication packet; a detection unit that detects the synchronization data before all of the received communication packets received by the packet reception unit has been read in; and a signal output unit that outputs a synchronization signal used for establishing synchronization of the timing of the processing related to photography on the basis of detection by the detection unit of the synchronization data.