A drive transmission system includes a shaft member storing grease in a shaft outer circumferential small diameter section. A drive transmission gear is provided including a gear inner circumferential sliding section and a gear inner circumferential large diameter section. A gear moving device is provided to move the drive transmission gear reciprocally along the shaft member in a shaft direction. A restriction device is provided to restrict a movement range of the drive transmission gear along the shaft member in the shaft direction to enable the gear inner circumferential large diameter section to face the shaft outer circumferential small diameter section substantially continuously.