PURPOSE: To output an alarm or the like immediately when any abnormality is caused, by arranging an input signal pulse detector, an output signal pulse detector, a delay time detector and a delay time discriminator to always monitor a delay between an input signal and an output signal of a pulse distributor.

CONSTITUTION: An input signal pulse detector 10 and an output signal pulse detector 12 are connected to the input side and the output side of a pulse distributor 1 respectively so as to receive signals inputted from channels. A delay time detector 14 connected to the output sides of the detectors 10 and 12 receives an input signal pulse from the detector 10 and an output signal pulse from the detector 12 as input and outputs a pulse based on a delay time difference between both the signals to a delay time discriminator 16. Here, when the delay time between the input signal pulse and the output signal pulse shows an abnormality, the discriminator 16 outputs an abnormality signal to a latch circuit or the like to latch this signal. The output of the latch circuit is displayed on a proper display unit or activates an alarm.