An external strobe device for connecting to an image-capturing apparatus. The image capturing apparatus includes a housing, a second electrical port, and a first signal port. The external strobe device includes a housing, a strobe module, a battery module, a first electrical port for connecting to the second electrical port and transmitting electric power produced by the battery module to the second electrical port to supply the electric power of the image-capturing apparatus, and a transformer for transforming an output voltage of the battery module into a standard voltage of the strobe module and into the standard voltage of the image-capturing apparatus.