PURPOSE: To miniaturize circuit size and to reduce monitoring process quantity of CPU than before, relating to a change point detecting circuit which monitors change points of multiple signals.

CONSTITUTION: N numbers of input signal are duplexed at a duplexing part 2. The value directly coming from the duplexing part 2 is compared with the value coming through a delay circuit 3. If change is found in input, it is sent the an FIFO 6 as a writing signal. At the time, the numerical value corresponding to the terminal number is written in the FIFO 6 and then is read by a CPU 7 for detecting a change point.