A gear system is provided. The gear system includes a driven gear, which is rotated by driving force from a driving gear, a base member to support the driven gear, and a bearing structure, including a shaft and a shaft hole to rotatably support the shaft, by which the driven gear is rotatably attached to the base member. One of the shaft and the shaft hole is provided to the driven gear, and the other of the shaft and the shaft hole is provided to the base member. The bearing structure has a lubricant reservoir in a slidable section, in which the shaft and the shaft hole are slidably in contact with each other when the driven gear is rotated by the driving force from the driving gear, the lubricant reservoir containing lubricant to lubricate the slidable section.