PURPOSE: To keep the time resolution against state change to a prescribed accuracy, by preventing the interruption from each input means to a processor excepting for the production of an enable signal.

CONSTITUTION: An interruption enable signal is applied from the processor 1B to a state change detecting input card 5B and an AND gate 16 enabling an output of an interruption SRFF13 only when an interruption enable signal 15 is set in the card 5B. Thus, the state change of an input data 10 is detected at a state change detecting circuit 9 and the SRFF13 is set, then the operation of the AND gate 16 is suppressed until the interruption enable signal 15 is outputted, allowing to prevent the interruption to the processor 1B.