An image forming device and an operating method are provided. The operating method included outputting a notification indicating that a cartridge in an image forming device needs to be refilled with toner, in accordance with the notification, performing a preparatory operation for entering a refill mode when it is determined that an operation mode of the image forming device is to be switched to the refill mode for refilling the cartridge with toner, when the preparatory operation is completed, controlling the image forming device such that only an operation related to the toner refilling is performed according to the refill mode, and when the refill mode is terminated, switching the operation mode of the image forming device to a job mode for performing a predetermined job in the image forming device.