PURPOSE: To measure chattering sustanining time with a simple circuit constitution by generating clock pluses through closing of the contacts to be measured and reading these with the chattering pulses generated through closing of said contacts.

CONSTITUTION: When the contacts to be measured close, a monostable multi 5 goes ON. A clock pulse generator 7 then generates a clock pulse. This pulse is inputted to a series input parallel output register 8. At each input, each Q output subsequently inverts and inputs to the inputs D1... of a parallel input parallel output register 6 corresponding to respective Q outputs. When at the same time the chattering generated by closing the contacts 1 to be measured is supplied to the register 6, the signal being supplied to the D input of the register 6 at that time is read at the negative edge of said chattering pulse and the same state as that of said input signal is outputted to the Q' output corresponding to the D input. Namely, if the period of the clock pulse is Tw, it turns out that the sustaining time of the chattering had been between m.Tw and (m+1).Tw. Hence, a display LED is driven by the Q' output of the register 6.