A diagnostic system that effectively presents optimum products to the users by effectively using information about the use history of an image forming apparatus used by the users and other information specific to the image forming apparatus that may be stored in advance. The diagnostic system includes a management device that receives and manages management information including at least information of print volume of an image forming apparatus for a predetermined period, a determination device that determines an optimum image forming apparatus based on the information of print volume in the predetermined period managed by the management device, and a notification device that notifies information indicative of the optimum image forming apparatus determined by the determination device to an information processing apparatus that is capable of communication via a communication line.