An image forming system includes a plurality of image forming devices connected in data communication with each other via a network. Each of the image forming devices includes a storage unit, an operational unit, and a controller. If one user logs into a first image forming device among the image forming devices, a controller of the first image forming device checks for the existence of a second image forming device into which the user has logged. If the controller of the first image forming device determines the second image forming device into which the user has logged, the controller transmits a logout instruction of the user to the second image forming device.