PURPOSE: To measure the presence of the generation of trigger jitter by simple constitution by providing a double pulse generation circuit for outputting two pulses having the time difference corresponding to the 90° phase difference of a sine wave signal therebetween according to a trigger pulse.

CONSTITUTION: A double pulse generating circuit 5 outputs two pulses S4 having the time different T corresponding to the 90° phase difference of a sine wave signal according to the trigger pulse S3 of a trigger control circuit 4. Herein, by setting a delay time by the delay circuit 10 of the circuit 5, a pulse width is set so that the pulses become abnormal when the circuit 4 is in a metastable state. The amplitudes Asinωt, Acosωt, of sine wave signals at the points of time when the respective pulses are outputted are converted to digital signals X, Y on the basis of a signal S4 by an A/D converter 3. An operational control part 6 calculates the square sum of the signals X, Y and compares the measured result at the time of measurement with the square sum at the time of normal operation to judge the presence of the generation of trigger jitter. When it is judged that trigger jitter is generated, the data thereof is removed from waveform regeneration operation.