PURPOSE: To improve measuring accuracy, by measuring periods of pulse genera tion synchronized with leading and trailing output pulses and determining a difference of them.
CONSTITUTION: An output of an edge trigger monostable multivibrator 15 is introduced into an input side of an exclusive OR circuit 16 as a leasing and trailing selecting circuit through a specimen device and an output of the circuit 16 is supplied as a trigger pulse of the monostable multivibrator 15. A selecting signal of a terminal 17 is introduced into the other side of the circuit 16. In this construction, the selecting signal of the terminal 17 is brought down to a lower level, an output pulse of the device 13 passes through the circuit 16 unprocessed and the multivibrator 15 is triggered on the front edge of the passing pulse and a vibrating loop of a pulse synchronized with the leading time of the output pulse is constructed. Further, when the selecting signal is brought to a high level, an output pulse of the device 13 is subjected to reversal of polarity in the circuit 16 and a vibrating loop of a pulse synchronized with the trailing time of the output pulse is constructed. A vibrating period synchronized with these leading and trailing times is measured by a period meter 18 and the pulse width is measured by a difference of both measured periods.