An image forming system includes an image forming apparatus that includes process units for different colors and a lifetime management device that manages lifetime information on each unit of the image forming apparatus. The lifetime management device counts the number of prints produced by the image forming apparatus with respect to each of photoconductor units and developing units in the process units, and measures an operation amount unique to the respective units. Based on the number of prints, service life of each unit and operation amount, the lifetime management device calculates the remaining lifetime of each unit.