A drive transmission system includes a drive source and a gear. The drive source includes a rotating shaft, a magnet supported by the rotating shaft, and plural electromagnets. The plural electromagnets are arranged in a circumferential direction of the rotating shaft, and surround the magnet. The drive source drives the rotating shaft to rotate by a predetermined rotation angle by exciting at least one of the plural electromagnets in accordance with an input of an input signal and by periodically changing a magnetic pole to which each of the plural electromagnets is excited in response to an input of the input signal. The gear is supported by the rotating shaft.