1. An image forming apparatus in which program objects represented in byte codes can be loaded, the program objects providing services for image forming processing, said apparatus comprising: a hardware resource unit including at least one of a printing unit and an image pickup unit; and a memory unit configured to store (i) an operating system, (ii) an interpreter which runs on the operating system and interprets the program objects represented in byte codes, (iii) a driver program for controlling image forming processing, and (iv) the program objects represented in byte codes, wherein the program objects stored in said memory unit perform a message communication, wherein the driver program operates said hardware resource unit, and wherein function programs each serving as an API (Application Programming Interface) are (a) defined between the program objects and the driver program, (b) used commonly by the program objects, and (c) interpreted by the interpreter.