PURPOSE: To conduct the measurement with less error, by determining position of a crossing point between an input signal and an output signal on an oscilloscope picture and also by calculating time delay from a measurement value of frequency of the output signal using a counter.

CONSTITUTION: An oscillator 4 which generates variable-frequency pulses is connected to an input terminal 2 of a device 1 to be measured, the frequency counter 7 is connected to an output terminal 3, and the oscilloscope 5 is connected between the input terminal 2 and the output terminal 3. And by varying the oscillation frequency of the oscillator 4, it is indicated on the oscilloscope picture that a point of 1/2 amplitude at the input signal rise time coincides with a point of 1/2 amplitude at the output signal fall time. And then, under this condition, the frequency is measured by the counter 7 to calculate the time delay. And therefore, it is possible to prevent introduction of measurement error even at the time of a large time delay and also to conduct the measurement with less error.