In order to maintain image quality with many noise factors, we should consider improvement of system robustness, decreasing of noise factors and the process control system. Moreover in an MFP used in an office, compact size and lower cost are also important issues.This paper describes a basic idea of process control system of an electrophotographic system, several inventions incorporated in a compact MFP and some issues to be investigated in future. There are some objectives of the process control, however maintaining image density is one of the critical issues and it is focused in this paper.Several sensors are used to detect characteristics such as environmental conditions, toner amount on a substrate. The process parameters are controlled according to the detected signals so that change of image density can be minimized.In a compact MFP (Aficio2238), several technologies are incorporated to achieve both stability of image density and the compact size. One is the binary exposure (1 bit) and smaller diameter of the LD beam. This is effective to improve the system robustness. Another is a simple control system. Number of sensors is minimized and some compensations of sensors are carried out without any special adjustments.In future, less waiting time, minimizing the changes between MFPs and establishment of suitable balance of the three directions are important items.