PURPOSE: To fully effect the function of an injection system by selectively applying one program as the occasion demands, from a plurality of different control programs by means of a switch or so.

CONSTITUTION: A plurality of different programs which meet individual demands (complete one program or a part of it) are prepared in advance and as the occasion demands, they are selected for application by the change-over operation of a switch or so. The conventional injection system can be used almost completely as it is so that the performance of the injection system may be inproved in a short duration and at low expenditure.