This invention increases the design efficiency of an upper layer such as a job control means. To accomplish this, an image processing apparatus having a plurality of types of external interfaces (a USB and LAN) different in protocol has an external interface adaptor 203 which dynamically allocates external interfaces as objects of processing to lower layer IDs within a predetermined range, and a job controller 202 which controls execution of various types of jobs by using the lower layer IDs, and a value which the lower layer ID can take is constant regardless of the type of external interface.