An image forming system includes an image processor, a print engine, optional units, and a serial signal line. The print engine includes a device managing a variety of information including data relating to its own status and data relating to status of the otpional units. The variety of information are represented by corresponding codes based on total status of the image forming means and the optional units. Each of the optional units includes a device for managing the aforementioned data relating to its own status, and a device for sending the print engine the data relating to its own status.