In an image forming system in which a printing device is communicably connected to a server and a terminal, an automatic determination is performed to determine whether or not print data created by the terminal needs to be stored in a memory for placing the data in a reprintable condition. The print data stored in the memory can be reprinted without need for resending the same print data from the terminal or server to the printing device. The automatic determination is, for example, performed by referring to the header of the print data and determining whether the print data is from the terminal or the server.