1. An image converting system comprising two or more image converting devices, each of the image converting devices including an image input device, an image converter, and a line memory, wherein the two or more image converting devices output conversion results to a storage medium common to each other while synchronizing with each other, wherein each of said image converting devices converts input image in accordance with a conversion specifying means, wherein said synchronizing is realized by providing said conversion specifying means with interrupt instructions, and wherein said interrupt instructions are stored in said storage medium.