PURPOSE: To output the fault detecting result in real time by providing a shared counter whose count value is increased or decreased when one of fault information processing tasks detects the changing point of the fault input information.

CONSTITUTION: Plural (n) pieces of application programs are provided opposite to (n) pieces of fault information processing tasks An (n = 1 - n) and carried out in time division by an operating system. The tasks A1 - An monitor the changing point of the fault input information and adds together the value of a shared counter B when a fault occurs. Then the information showing the absence of a fault with the value of the counter B equal to '0' and the presence of the fault with the value of the counter B equal to '1 - n' respectively are outputted. Thus the fault information is outputted in real time to the fault input information.