PURPOSE: To eliminate influence of noise by letting an RAM count the number of offerings using the timer offering emitted by a timer counter for count of system clock pulses, providing a long-time interval longer than the width of noise pulses, and by shortening this interval when the data have changed.

CONSTITUTION: Pulses made by a system clock in a micro-computor 1 are counted by a timer counter 1e, and timer offerings generated by overflow are input to perform the offering flow program instead of main flow. When the number of offerings has attained a value corresponding to the input time of monitoring, the data shall be substituted by new data, which shall be compared with the memory data of an RAM 1c, and if they are in coincidence the memory in the RAM 1c are renewed and, on the other hand, if they are not in coincidence the input data shall be renewed to shorten the time of offering. Thus, influence of noises in soft ware can be eliminated without furnishing any special circuitry.